An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

Marcus Baumann and
Ian R. Baxendale

Review
Published 30 Oct 2013

1115 Accesses

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1. Graphical Abstract
2. Scheme 1: Scaled industrial processes for the synthesis of simple pyridines.
  
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3. Scheme 2: Synthesis of nicotinic acid from 2-methyl-5-ethylpyridine (1.11).
  
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4. Scheme 3: Synthesis of 3-picoline and nicotinic acid.
  
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5. Scheme 4: Synthesis of 3-picoline from 2-methylglutarodinitrile 1.19.
  
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6. Scheme 5: Picoline-based synthesis of clarinex (no yields reported).
  
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7. Scheme 6: Mode of action of proton-pump inhibitors and structures of the API’s.
  
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8. Scheme 7: Hantzsch-like route towards the pyridine rings in common proton pump inhibitors.
  
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9. Figure 1: Structures of rosiglitazone (1.40) and pioglitazone (1.41).
  
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10. Scheme 8: Synthesis of rosiglitazone.
  
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11. Scheme 9: Syntheses of 2-pyridones.
  
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12. Scheme 10: Synthesis and mechanism of 2-pyrone from malic acid.
  
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13. Scheme 11: Polymer-assisted synthesis of rosiglitazone.
  
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14. Scheme 12: Synthesis of pioglitazone.
  
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15. Scheme 13: Meerwein arylation reaction towards pioglitazone.
  
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16. Scheme 14: Route towards pioglitazone utilising tyrosine.
  
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17. Scheme 15: Route towards pioglitazone via Darzens ester formation.
  
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18. Scheme 16: Syntheses of the thiazolidinedione moiety.
  
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19. Scheme 17: Synthesis of etoricoxib utilising Negishi and Stille cross-coupling reactions.
  
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20. Scheme 18: Synthesis of etoricoxib via vinamidinium condensation.
  
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21. Figure 2: Structures of nalidixic acid, levofloxacin and moxifloxacin.
  
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22. Scheme 19: Synthesis of moxifloxacin.
  
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23. Scheme 20: Synthesis of (S,S)-2,8-diazabicyclo[4.3.0]nonane 1.105.
  
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24. Scheme 21: Synthesis of levofloxacin.
  
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25. Scheme 22: Alternative approach to the levofloxacin core 1.125.
  
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26. Figure 3: Structures of nifedipine, amlodipine and clevidipine.
  
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27. Scheme 23: Mg₃N₂-mediated synthesis of nifedipine.
  
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28. Scheme 24: Synthesis of rac-amlodipine as besylate salt.
  
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29. Scheme 25: Aza Diels–Alder approach towards amlodipine.
  
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30. Scheme 26: Routes towards clevidipine.
  
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31. Figure 4: Examples of piperidine containing drugs.
  
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32. Figure 5: Discovery of tiagabine based on early leads.
  
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33. Scheme 27: Synthetic sequences to tiagabine.
  
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34. Figure 6: Structures of solifenacin (2.57) and muscarine (2.58).
  
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35. Scheme 28: Enantioselective synthesis of solifenacin.
  
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36. Figure 7: Structures of DPP-4 inhibitors of the gliptin-type.
  
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37. Scheme 29: Formation of inactive diketopiperazines from cis-rotameric precursors.
  
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38. Figure 8: Co-crystal structure of carmegliptin bound in the human DPP-4 active site (PDB 3kwf).
  
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39. Scheme 30: Improved route to carmegliptin.
  
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40. Figure 9: Structures of lamivudine and zidovudine.
  
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41. Scheme 31: Typical routes accessing uracil, thymine and cytosine.
  
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42. Scheme 32: Coupling between pyrimidones and riboses via the Vorbrüggen nucleosidation.
  
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43. Scheme 33: Synthesis of lamivudine.
  
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44. Scheme 34: Synthesis of raltegravir.
  
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45. Scheme 35: Mechanistic studies on the formation of 3.22.
  
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46. Figure 10: Structures of selected pyrimidine containing drugs.
  
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47. Scheme 36: General preparation of pyrimidines and dihydropyrimidones.
  
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48. Scheme 37: Synthesis of imatinib.
  
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49. Scheme 38: Flow synthesis of imatinib.
  
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50. Scheme 39: Syntheses of erlotinib.
  
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51. Scheme 40: Synthesis of erlotinib proceeding via Dimroth rearrangement.
  
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52. Scheme 41: Synthesis of lapatinib.
  
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53. Scheme 42: Synthesis of rosuvastatin.
  
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54. Scheme 43: Alternative preparation of the key aldehyde towards rosuvastatin.
  
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55. Figure 11: Structure comparison between nicotinic acetylcholine receptor agonists.
  
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56. Scheme 44: Syntheses of varenicline and its key building block 4.5.
  
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57. Scheme 45: Synthetic access to eszopiclone and brimonidine via quinoxaline intermediates.
  
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58. Figure 12: Bortezomib bound in an active site of the yeast 20S proteasome ([114], pdb 2F16).
  
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59. Scheme 46: Asymmetric synthesis of bortezomib.
  
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60. Figure 13: Structures of some prominent piperazine containing drugs.
  
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61. Figure 14: Structural comparison between the core of aplaviroc (4.35) and a type-1 β-turn (4.36).
  
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62. Scheme 47: Examplary synthesis of an aplaviroc analogue via the Ugi-MCR.
  
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63. Scheme 48: Syntheses of azelastine (5.1).
  
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64. Figure 15: Structures of captopril, enalapril and cilazapril.
  
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65. Scheme 49: Synthesis of cilazapril.
  
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66. Figure 16: Structures of lamotrigine, ceftriaxone and azapropazone.
  
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67. Scheme 50: Synthesis of lamotrigine.
  
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68. Scheme 51: Alternative synthesis of lamotrigine (no yields reported).
  
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69. Figure 17: Structural comparison between imiquimod and the related adenosine nucleoside.
  
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70. Scheme 52: Conventional synthesis of imiquimod (no yields reported).
  
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71. Scheme 53: Synthesis of imiquimod.
  
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72. Scheme 54: Synthesis of imiquimod via tetrazole formation (not all yields reported).
  
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73. Figure 18: Structures of various anti HIV-medications.
  
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74. Scheme 55: Synthesis of abacavir.
  
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75. Figure 19: Structures of diazepam compared to modern replacements.
  
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76. Scheme 56: Synthesis of ocinaplon.
  
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77. Scheme 57: Access to zaleplon and indiplon.
  
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78. Scheme 58: Different routes towards the required N-methylpyrazole 6.65 of sildenafil.
  
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79. Scheme 59: Polymer-supported reagents in the synthesis of key aminopyrazole 6.72.
  
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80. Scheme 60: Early synthetic route to sildenafil.
  
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81. Scheme 61: Convergent preparations of sildenafil.
  
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82. Figure 20: Comparison of the structures of sildenafil, tadalafil and vardenafil.
  
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83. Scheme 62: Short route to imidazotriazinones.
  
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84. Scheme 63: Alternative route towards vardenafils core imidazotriazinone (6.95).
  
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85. Scheme 64: Bayer’s approach to the vardenafil core.
  
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86. Scheme 65: Large scale synthesis of vardenafil.
  
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87. Scheme 66: Mode of action of temozolomide (6.105) as methylating agent.
  
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88. Scheme 67: Different routes to temozolomide.
  
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89. Scheme 68: Safer route towards temozolomide.
  
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90. Figure 21: Some unreported heterocyclic scaffolds in top market drugs.
  
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Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

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Visible-light-mediated copper photocatalysis for organic syntheses

Yajing Zhang,
Qian Wang,
Zongsheng Yan,
Donglai Ma and
Yuguang Zheng

Review
Published 12 Oct 2021

592 Accesses

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1. Graphical Abstract
2. Scheme 1: Photoredox catalysis mechanism of [Ru(bpy)₃]²⁺.
  
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3. Scheme 2: Photoredox catalysis mechanism of Cu^I.
  
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4. Scheme 3: Ligands and Cu^I complexes.
  
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5. Scheme 4: Mechanism of Cu^I-based photocatalysis.
  
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6. Scheme 5: Mechanisms of Cu^I–substrate complexes.
  
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7. Scheme 6: Mechanism of Cu^II-base photocatalysis.
  
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8. Scheme 7: Olefinic C–H functionalization and allylic alkylation.
  
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9. Scheme 8: Cross-coupling of unactivated alkenes and CF₃SO₂Cl.
  
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10. Scheme 9: Chlorosulfonylation/cyanofluoroalkylation of alkenes.
  
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11. Scheme 10: Hydroamination of alkenes.
  
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12. Scheme 11: Cross-coupling reaction of alkenes, alkyl halides with nucleophiles.
  
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13. Scheme 12: Cross-coupling of alkenes with oxime esters.
  
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14. Scheme 13: Oxo-azidation of vinyl arenes.
  
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15. Scheme 14: Azidation/difunctionalization of vinyl arenes.
  
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16. Scheme 15: Photoinitiated copper-catalyzed Sonogashira reaction.
  
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17. Scheme 16: Alkyne functionalization reactions.
  
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18. Scheme 17: Alkynylation of dihydroquinoxalin-2-ones with terminal alkynes.
  
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19. Scheme 18: Decarboxylative alkynylation of redox-active esters.
  
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20. Scheme 19: Aerobic oxidative C(sp)–S coupling reaction.
  
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21. Scheme 20: Copper-catalyzed alkylation of carbazoles with alkyl halides.
  
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22. Scheme 21: C–N coupling of organic halides with amides and aliphatic amines.
  
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23. Scheme 22: Copper-catalyzed C–X (N, S, O) bond formation reactions.
  
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24. Scheme 23: Arylation of C(sp²)–H bonds of azoles.
  
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25. Scheme 24: C–C cross-coupling of aryl halides and heteroarenes.
  
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26. Scheme 25: Benzylic or α-amino C–H functionalization.
  
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27. Scheme 26: α-Amino C–H functionalization of aromatic amines.
  
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28. Scheme 27: C–H functionalization of aromatic amines.
  
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29. Scheme 28: α-Amino-C–H and alkyl C–H functionalization reactions.
  
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30. Scheme 29: Other copper-photocatalyzed reactions.
  
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31. Scheme 30: Cross-coupling of oxime esters with phenols or amines.
  
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32. Scheme 31: Alkylation of heteroarene N-oxides.
  
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Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

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In-depth characterization of self-healing polymers based on π–π interactions

Josefine Meurer,
Julian Hniopek,
Johannes Ahner,
Michael Schmitt,
Jürgen Popp,
Stefan Zechel,
Kalina Peneva and
Martin D. Hager

Full Research Paper
Published 29 Sep 2021

569 Accesses

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1. Graphical Abstract
2. Scheme 1: Schematic representation of the polymer synthesis of P1 and P2.
  
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3. Figure 1: DSC-analysis of the polymers P1 and P2 (second heating and cooling cycle; 20 K/min for heating and ...
  
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4. Figure 2: DMTA analysis of P1 and P2 showing the transition at around 130 °C due to the reversible π–π intera...
  
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5. Figure 3: Frequency sweeps of polymers P1 (left) and P2 (right).
  
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6. Figure 4: Temperature dependent IR spectra of P1 drop casted on KBr in the C=C (1570–1605 cm⁻¹) and C=O stret...
  
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7. Figure 5: Schematic representation of the first healing of P1 at 150 °C.
  
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Beilstein J. Org. Chem. 2021, 17, 2496–2504, doi:10.3762/bjoc.17.166

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Cryogels: recent applications in 3D-bioprinting, injectable cryogels, drug delivery, and wound healing

Luke O. Jones,
Leah Williams,
Tasmin Boam,
Martin Kalmet,
Chidubem Oguike and
Fiona L. Hatton

Review
Published 14 Oct 2021

539 Accesses

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1. Graphical Abstract
2. Figure 1: Schematic representation of the process of aqueous cryogel formation, using (a) monomers/small mole...
  
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3. Figure 2: Microarchitecture of gelatin cryogels. (A) Surface and cross-sectional SEM micrographs of highly po...
  
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4. Figure 3: Principle of 3D-cryogel printing. A) Illustration of 3D-printing of cryogels. B) Illustration of th...
  
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5. Figure 4: Illustration of the production of the injectable multifunctional composite, comprised of alginate c...
  
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6. Figure 5: Digital and SEM photographs of PETEGA cryogel at 20 °C (top) and 50 °C (bottom), synthesised via UV...
  
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7. Figure 6: Cell morphology of T47D breast cancer cells cultured in HA cryogels. (A) Schematic representation o...
  
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8. Figure 7: Preparation of PDMA/β-CD cryogel via cryogenic treatment and photochemical crosslinking in frozen s...
  
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9. Figure 8: (A) Healing rate of wounds treated with autoclaved CG11 cryogels and those treated with 70% ethanol...
  
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10. Figure 9: In vivo haemostatic capacity evaluation of the cryogels. Blood loss (a) and haemostatic time (b) in...
  
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Beilstein J. Org. Chem. 2021, 17, 2553–2569, doi:10.3762/bjoc.17.171

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Copper-catalyzed monoselective C–H amination of ferrocenes with alkylamines

Zhen-Sheng Jia,
Qiang Yue,
Ya Li,
Xue-Tao Xu,
Kun Zhang and
Bing-Feng Shi

Letter
Published 28 Sep 2021

524 Accesses

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1. Graphical Abstract
2. Scheme 1: 3d-Transition-metal-catalyzed C–H functionalization to access functionalized ferrocenes.
  
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3. Scheme 2: Scope of ferrocenes with morpholine.
  
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4. Scheme 3: Scope of various amines with 1a.
  
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5. Scheme 4: Synthetic applications.
  
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6. Scheme 5: Mechanistic experiments.
  
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Beilstein J. Org. Chem. 2021, 17, 2488–2495, doi:10.3762/bjoc.17.165

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Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation

Azra Kocaarslan,
Zafer Eroglu,
Önder Metin and
Yusuf Yagci

Full Research Paper
Published 23 Sep 2021

507 Accesses

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1. Graphical Abstract
2. Figure 1: Structures of azide and alkyne functional molecules and polymers used in the photoinduced CuAAC rea...
  
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3. Figure 2: UV–vis spectra of Cu^ICl, Cu^IICl₂ and BPNs.
  
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4. Figure 3: a) ¹H NMR spectra of the model reaction between benzyl azide (Az-1) and phenylacetylene (Alk-3) bef...
  
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5. Scheme 1: Proposed mechanism for photoinduced CuAAC reaction using exfoliated BPNs.
  
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6. Figure 4: a) ¹H NMR spectrum of chain end modified PCL-Anth; b) UV–vis spectra of (azidomethyl)anthracene (bl...
  
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7. Scheme 2: Synthesis of PS-b-PCL block copolymer via exfoliated BPNs-mediated photoinduced CuAAC reaction.
  
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8. Figure 5: a) GPC traces of PS-Az, PCL-Alk and block copolymer (Ps-b-PCL) b) ¹H NMR spectrum of the block copo...
  
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9. Scheme 3: Preparation of the cross-linked polymer by CuAAC reaction using multifunctional monomers, Az-3 and ...
  
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10. Figure 6: a) DSC thermogram of photoinduced synthesis of nanocomposite networks (heating rate: 10 °C/min). b)...
  
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11. Figure 7: (a, b) TEM images of cross-linked polymer at two different magnifications, c) HAADF-STEM image and ...
  
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Beilstein J. Org. Chem. 2021, 17, 2477–2487, doi:10.3762/bjoc.17.164

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The in situ generation and reactive quench of diazonium compounds in the synthesis of azo compounds in microreactors

Faith M. Akwi and
Paul Watts

Full Research Paper
Published 06 Sep 2016

468 Accesses

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1. Graphical Abstract
2. Scheme 1: PTSA-catalyzed diazotization and azo coupling reaction.
  
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3. Scheme 2: Ferric hydrogen sulfate (FHS) catalyzed azo compound synthesis.
  
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4. Scheme 3: Synthesis of azo compounds in the presence of silica supported boron trifluoride.
  
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5. Scheme 4: Phase transfer catalyzed azo coupling of 5-methylresorcinol in microreactors.
  
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6. Scheme 5: Synthesis of yellow pigment 12 in a micro-mixer apparatus.
  
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7. Scheme 6: Continuous flow synthesis of Sudan II azo dye in LTF-MS microreactors.
  
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8. Figure 1: pH profile plot at constant flow rate of 0.03 mL/min.
  
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9. Figure 2: pH profile plot at a constant flow rate of 0.7 mL/min.
  
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10. Scheme 7: Azo coupling reaction under acidic conditions.
  
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11. Figure 3: pH profile plot at a constant flow rate of 0.03 mL/min.
  
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12. Figure 4: pH profile plot at constant flow rate of 0.7 mL/min.
  
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13. Figure 5: Temperature profile plot at constant pH 5.66.
  
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14. Figure 6: Schematic representation of the microreactor set up.
  
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15. Figure 7: Schematic representation of the microreactor set up.
  
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16. Figure 8: Scaled up microreactor set up: PTFE tubing i.d. 1.5 mm a) Chemyx Fusion 100 classic syringe pump, b...
  
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Beilstein J. Org. Chem. 2016, 12, 1987–2004, doi:10.3762/bjoc.12.186

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Synthesis of new substituted 7,12-dihydro-6,12-methanodibenzo[c,f]azocine-5-carboxylic acids containing a tetracyclic tetrahydroisoquinoline core structure

Agnieszka Grajewska,
Maria Chrzanowska and
Wiktoria Adamska

Full Research Paper
Published 07 Oct 2021

460 Accesses

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1. Graphical Abstract
2. Figure 1: Natural isopavine alkaloids and synthetic derivatives of isopavine.
  
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3. Figure 2: The structure and numbering of dihydromethanodibenzoazocine.
  
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4. Scheme 1: The Petasis reaction and the Pomeranz–Fritsch–Bobbitt cyclization.
  
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5. Scheme 2: The synthesis of 7,12-dihydro-6,12-methanodibenzo[c,f]azocine-5-carboxylic acids via a combination ...
  
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6. Scheme 3: Synthesis of N-benzylated aminoacetaldehyde acetals 3a–e. Conditions: a) reaction run in EtOH; b) r...
  
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7. Scheme 4: Synthesis of amino acids 6a–g.
  
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8. Scheme 5: Synthesis of dihydromethanodibenzoazocine-5-carboxylic acids 7a–f. Conditions: a) 20% HCl, rt, 24 h...
  
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9. Scheme 6: Synthesis of TA-073.
  
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10. Scheme 7: Reaction of 6a with 4% aqueous HCl solution in THF and with 20% aqueous HCl solution. Conditions: a...
  
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11. Scheme 8: Three pathways of the synthesis of 12, the decarboxylated analogue of 6a.
  
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12. Scheme 9: The chemical behavior of 12 in 4% aqueous HCl solution in THF and in 20% aqueous HCl solution.
  
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13. Scheme 10: A plausible mechanism of the reaction of 6a with 4% aqueous HCl solution in THF.
  
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Beilstein J. Org. Chem. 2021, 17, 2511–2519, doi:10.3762/bjoc.17.168

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Direct C(sp³)–H allylation of 2-alkylpyridines with Morita–Baylis–Hillman carbonates via a tandem nucleophilic substitution/aza-Cope rearrangement

Siyu Wang,
Lianyou Zheng,
Shutao Wang,
Shulin Ning,
Zhuoqi Zhang and
Jinbao Xiang

Letter
Published 01 Oct 2021

457 Accesses

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1. Graphical Abstract
2. Scheme 1: The benzylic C(sp³)–H allylic alkylation reactions of 2-alkylpyridines.
  
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3. Scheme 2: Mechanistic hypothesis of the alkylation reaction of 2-alkylpyridines with MBH carbonates.
  
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4. Scheme 3: Scope of MBH carbonates 2 with 2-picoline 1a. The reactions were performed using 1a (1.0 mmol, 2 eq...
  
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5. Scheme 4: Scope of 2-alkylpyridine 1 with MBH carbonate 2a. The reactions were performed using 1 (1.0 mmol, 2...
  
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Beilstein J. Org. Chem. 2021, 17, 2505–2510, doi:10.3762/bjoc.17.167

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Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

Lukas Hintermann

Full Research Paper
Published 28 Aug 2007

456 Accesses

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1. Graphical Abstract
2. Figure 1: The carbenes IPr, IMes, IXy and their imidazolium salt precursors
  
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3. Scheme 1: Synthetic routes to and diazadiene precursors for imidazolium salts.
  
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4. Scheme 2: The imidazolium salt synthesis as a 1, 5-dipolar electrocyclization.
  
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5. Scheme 3: Potential side-reactions in the imidazolium salt synthesis.
  
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Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

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An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

Visible-light-mediated copper photocatalysis for organic syntheses

In-depth characterization of self-healing polymers based on π–π interactions

Cryogels: recent applications in 3D-bioprinting, injectable cryogels, drug delivery, and wound healing

Copper-catalyzed monoselective C–H amination of ferrocenes with alkylamines

Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation

The in situ generation and reactive quench of diazonium compounds in the synthesis of azo compounds in microreactors

Synthesis of new substituted 7,12-dihydro-6,12-methanodibenzo[c,f]azocine-5-carboxylic acids containing a tetracyclic tetrahydroisoquinoline core structure

Direct C(sp³)–H allylation of 2-alkylpyridines with Morita–Baylis–Hillman carbonates via a tandem nucleophilic substitution/aza-Cope rearrangement

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

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