Tandem Hock and Friedel–Crafts reactions allowing an expedient synthesis of a cyclolignan-type scaffold

• Viktoria A. Ikonnikova,
• Cristina Cheibas,
• Oscar Gayraud,
• Alexandra E. Bosnidou,
• Nicolas Casaretto,
• Gilles Frison and
• Bastien Nay

Beilstein J. Org. Chem. 2024, 20, 162–169, doi:10.3762/bjoc.20.15

• alternative mechanism, we envisionned a possible interconversion of 7 and 7’ through a [1,5]-sigmatropic rearrangement resulting in a hydrogen and cation shift towards 7’ (Scheme 4). To test this hypothesis, this rearrangement was computed at the DFT level. A cyclic transition state (TS) was found between

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• ]-sigmatropic rearrangement of the diazabicycle 47 to form the allylic carbazate intermediate 51. Nucleophilic attack of an organomagnesium, or organocuprate, in an anti SN2’ fashion on 52 furnish the final ring-opened product 49. The authors note the use of a carbamate protecting group was crucial for the

Improving the accuracy of ³¹P NMR chemical shift calculations by use of scaling methods

• William H. Hersh and
• Tsz-Yeung Chan

Beilstein J. Org. Chem. 2023, 19, 36–56, doi:10.3762/bjoc.19.4

• chemical shift of −181 ppm. Compound 32 underwent a stereospecific thermal [1,5]-sigmatropic rearrangement to bicyclic 33 exhibiting a 31P NMR chemical shift of −79 ppm. Pyrolysis of 33 at 480 °C gave isomeric 34 having a 31P NMR chemical shift of −14 ppm, while H2O2 oxidation of compounds 33 and 34 gave

Synthetic study toward tridachiapyrone B

• Morgan Cormier,
• Florian Hernvann and
• Michaël De Paolis

Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183

• by destabilizing the negative charge of the anion (Scheme 7c). Simply generated with Triton B (benzyltrimethylammonium hydroxide), the alcoholate of 17 smoothly (−20 °C to rt) underwent the [3,3]-sigmatropic rearrangement (75% conversion) directly affording 2,5-cyclohexadienone E-19 which was

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• ′-binaphthalenes (BINAMs) from achiral N,N′-binaphthylhydrazines (Scheme 1). In the presence of chiral phosphoric acids (CPA 1), the reaction undergoes a simple [3,3]-sigmatropic rearrangement, giving the corresponding products 2 in good yield (up to 88%) and enantioselectivity (up to 93:7 er). The density

• functional calculations showed that the chiral phosphoric acid proton forms an H-bond with nitrogen atoms of 1 and the phosphate acts as a chiral counterion, resulting in a [3,3]-sigmatropic rearrangement with controlled stereoselectivity [14][41]. In 2017, Tan and co-workers developed an organocatalytic

• materials and supramolecules. Important chiral phosphoric acid scaffolds used in this review. Atroposelective aryl–aryl-bond formation by employing a facile [3,3]-sigmatropic rearrangement. Atroposelective synthesis of axially chiral biaryl amino alcohols 5. The enantioselective reaction of quinone and 2

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• cyclization and minimizes the competitive 2-oxonia-[3,3]-sigmatropic rearrangement pathway. The reaction was highly stereoselective and afforded the cis-2,6-dihydropyran in the presence of Lewis acid FeCl3. From DFT calculations, the authors concluded that the Prins product is formed more rapidly than the α

• formal 2-oxonia-[3,3]-sigmatropic rearrangement. Furthermore, Markó and co-workers successfully synthesized 2,6-anti-configured THP starting from allylsilane 245, following diethylaluminium chloride-promoted ene reaction and condensation with an aldehyde 246 [102]. Expected ene adduct 247 was obtained as

Recent progress in the synthesis of homotropane alkaloids adaline, euphococcinine and N-methyleuphococcinine

• Dimas J. P. Lima,
• Antonio E. G. Santana,
• Michael A. Birkett and
• Ricardo S. Porto

Beilstein J. Org. Chem. 2021, 17, 28–41, doi:10.3762/bjoc.17.4

• approach consisted of a 3,3-sigmatropic rearrangement to give an all-carbon quaternary center, a ring-closing alkene metathesis to give an 8-membered ring, and the use of a single enantiomer of p-menthane-3-carboxaldehyde to make two natural alkaloids of opposite configuration. Firstly, (+)-euphococcinine

Metal-free synthesis of biarenes via photoextrusion in di(tri)aryl phosphates

• Hisham Qrareya,
• Lorenzo Meazza,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 3008–3014, doi:10.3762/bjoc.16.250

• Truce–Smiles rearrangement in aryl sulfonamides and aryl phenylsulfonates [44][45][46] or the [3,3]-sigmatropic rearrangement of sulfonium salts arising from the reaction of aryl sulfoxides and phenols [47]. To overcome this problem, the use of a metal catalyst (mainly Ni) was mandatory as reported for

Selective preparation of tetrasubstituted fluoroalkenes by fluorine-directed oxetane ring-opening reactions

• Clément Q. Fontenelle,
• Thibault Thierry,
• Romain Laporte,
• Emmanuel Pfund and
• Thierry Lequeux

Beilstein J. Org. Chem. 2020, 16, 1936–1946, doi:10.3762/bjoc.16.160

• olefination or defluorination reactions or a sigmatropic rearrangement, but these approaches are limited and do not allow the synthesis of tetrasubstituted fluoroalkenes with good control of their geometry [18][19][20][21]. In order to develop a selective synthesis for tetrasubstituted fluoroalkenes we

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• on a Diels–Alder cycloaddition, an intramolecular Mitsunobu reaction, a [3,3]-sigmatropic rearrangement, and a ring-closing metathesis. As an alternative to this approach, Clark et al. [86] efficiently performed a sequential Ru-catalyzed enyne metathesis in combination with a hydroboration, and an

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• intermediate. This species then undergoes [3,3]-sigmatropic rearrangement, positioning the allylic unit in a regio- and stereospecific manner, along with rearomatization to afford the products 357–360 (Scheme 57) [107]. The borylfluoromethylation of acrylamides, acrylates, and heteroaromatic-substituted alkenes

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• rearrangement; silyl ketene acetals; Introduction The Ireland–Claisen rearrangement is a reaction converting allyl esters to γ,δ-unsaturated carboxylic acids. Its key step is a [3,3]-sigmatropic rearrangement of a silyl ketene acetal, which is generated in situ by deprotonation of an allyl ester using a strong

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• ]-sigmatropic rearrangement of allyldiphenylphosphinites, obtained from (1R,2R,4S,5R)-3-methyleneneoisoverbanol and (1R,2R,3R,5R)-4-methyleneneoisopinocampheol, to allylphosphine oxides. Hydroxy groups were introduced stereoselectively through a hydroboration–oxidation reaction proceeding from the less hindered

• site providing a trans relationship between the hydroxy and the phosphine substituents. Keywords: isopinocamphone; monoterpenes; phosphines; [2,3]-sigmatropic rearrangement; verbanone; Introduction Chiral phosphorus compounds, despite many years of research, still enjoy unflagging interest of many

• [2,3]-sigmatropic rearrangement of an allylic diphenylphosphinite to the diphenylphosphine oxide (Scheme 4) [16]. Diphenylphosphinite 19 was formed in the reaction of allylic alcohol 6 with diphenylphosphine chloride in the presence of DMAP at −20 ºC. The temperature was raised to induce phosphinite’s

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• butenolide 70. The second one is the reaction of alicyclic alcohol 73 with dimethylformamide dimethylacetal to give an allylic amide by means of a [2,3]-sigmatropic rearrangement of a carbene intermediate. Epoxidation the allylic amide with m-CPBA gave 74, followed by lithium hexamethyldisilazide-induced β

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• ]. In this review, we shall exclusively focus on alternative strategies that rely either on a [2,3]-sigmatropic rearrangement (Scheme 1, reaction 4) or a [3,3]-sigmatropic rearrangement of cyclopropenylcarbinol derivatives (Scheme 1, reaction 5). These transformations have emerged as useful tools over

• to enantiomerically enriched cyclopropenylcarbinols [31], Marek et al. investigated other classes of transformations involving those latter strained analogs of allylic alcohols as substrates. In 2007, the [2,3]-sigmatropic rearrangement of cyclopropenylcarbinyl phosphinites was reported as a route to

• [2,3]-sigmatropic rearrangement of the in situ-generated phosphinites 2a–h. Primary or tertiary cyclopropenylcarbinols reacted equally well, as shown with the formation of phosphine oxides 3a (94%), 3b (93%) and 3c (87%). The [2,3]-sigmatropic rearrangement of phosphinites 2d–h derived from secondary

Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety

• Alex Frichert,
• Peter G. Jones and
• Thomas Lindel

Beilstein J. Org. Chem. 2018, 14, 2461–2467, doi:10.3762/bjoc.14.222

• would be the attack of triflinate as O-nucleophile at the cyclohexane carbon, followed by [2,3]-sigmatropic rearrangement [31]. Conclusion With the synthesis of the [8.4.0]bicycles 18 and 19 that contain a 1,3-cyclohexadiene partial structure, we have made progress towards the synthesis of a small group

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

Recent progress in the racemic and enantioselective synthesis of monofluoroalkene-based dipeptide isosteres

• Myriam Drouin and
• Jean-François Paquin

Beilstein J. Org. Chem. 2017, 13, 2637–2658, doi:10.3762/bjoc.13.262

• 11 was converted into the trichloroimidate, and heating in xylenes permitted a [3,3]-sigmatropic rearrangement. At this stage, the trichloroimidate was transformed into an NHBoc moiety. Deprotection of the alcohol followed by Jones oxidation gave the final dipeptide isostere 13. Taguchi and co

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• stable elemanolide that is even more stable than its (Z,E)-germacrane. Keywords: biogenesis; density functional theory; reaction mechanism; sigmatropic rearrangement; terpenes; Introduction Germacranes are biogenetic precursors of elemanes [1][2][3][4], because germacranes can be easily transformed

Study on the synthesis of the cyclopenta[f]indole core of raputindole A

• Nils Marsch,
• Mario Kock and
• Thomas Lindel

Beilstein J. Org. Chem. 2016, 12, 334–342, doi:10.3762/bjoc.12.36

• the catalyst solution through a pad of Celite prior to addition of the starting material to remove AgCl. In that way we reached an 81% yield of tricycle 50. The acetoxy group again formally underwent a 1,3-shift to the benzylic position, which may also be based on a [3,3]-sigmatropic rearrangement

Tandem processes promoted by a hydrogen shift in 6-arylfulvenes bearing acetalic units at ortho position: a combined experimental and computational study

• Mateo Alajarin,
• Marta Marin-Luna,
• Pilar Sanchez-Andrada and
• Angel Vidal

Beilstein J. Org. Chem. 2016, 12, 260–270, doi:10.3762/bjoc.12.28

• same stationary points that in path A with the sole difference of the respective first mechanistic steps. Path B starts with a [1,9]-H sigmatropic rearrangement through TS1-B leading to intermediate 10a’, which then transforms via the mechanistic paths commented above. The geometry of TS1-B (see Figure

• 6a could take place by a variety of alternative reaction paths according to a complicated mechanistic scheme. By analysing in detail the energy barriers computed for each mechanistic step, the energetically preferred path starts with a [1,9]-H sigmatropic rearrangement of the acetalic hydrogen atom

Synthesis of Xenia diterpenoids and related metabolites isolated from marine organisms

• Tatjana Huber,
• Lara Weisheit and
• Thomas Magauer

Beilstein J. Org. Chem. 2015, 11, 2521–2539, doi:10.3762/bjoc.11.273

• acetylide to the carbonyl group of 69, followed by desilylation under basic conditions gave rise to (±)-ethynylcarbinol, which was separated by chiral HPLC. The desired diastereomer was then transformed to benzene sulfinate ester 70. A palladium-catalyzed [2,3]-sigmatropic rearrangement formed an isomeric

• prepared by regioselective reduction of the carbonyl group, silylation of the resulting alcohol and further reduction of the enone moiety. An ensuing transetherification of alcohol 59 with ethyl vinyl ether gave an allyl vinyl ether, which underwent a magnesium perchlorate-promoted [1,3]-sigmatropic

• rearrangement [41] to afford an aldehyde that was converted to dimethylacetal 60. The following epoxidation proceeded with good stereoselectivity (α/β ≈ 11:1) and the regioselective opening of the epoxide moiety using lithium cyanide afforded a β-hydroxy nitrile in a trans-diaxial arrangement. Under basic

Selected synthetic strategies to cyclophanes

• Sambasivarao Kotha,
• Mukesh E. Shirbhate and
• Gopalkrushna T. Waghule

Beilstein J. Org. Chem. 2015, 11, 1274–1331, doi:10.3762/bjoc.11.142

Attempts to prepare an all-carbon indigoid system

• Şeref Yildizhan,
• Henning Hopf and
• Peter G. Jones

Beilstein J. Org. Chem. 2015, 11, 363–372, doi:10.3762/bjoc.11.42

• [22][23]. The molecular packing is devoid of striking features. As far as the mode of formation of 23 is concerned, the isomerization formally is a [3.3]sigmatropic rearrangement (Cope rearrangement). Since the rearrangement of structurally similar compounds [24], including the parent system hexa-1,5

Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene

• Laurence Burroughs,
• John Ritchie,
• Mkhethwa Ngwenya,
• Dilfaraz Khan,
• William Lewis and
• Simon Woodward

Beilstein J. Org. Chem. 2015, 11, 273–279, doi:10.3762/bjoc.11.31

• , substituted phenyl, 2-thienyl) to ortho-C6H4(CHO)2 undergo cascades to tetracenes on simple admixture of LiHDMS, CS2 and MeI. Acene formation proceeds by [3,3]-sigmatropic rearrangement of xanthate anions followed by 6π electrocyclisations. The reactions are terminated by E2 or anionic Chugaev-type

• eliminations. Structural packing motifs and electronic properties are reported for the tetracenes. Keywords: allenes; anionic Chugaev rearrangement; anionic sigmatropic rearrangement; tetracene properties; X-ray structures; Introduction In recent years polyacenes, especially tetra- and pentacenes, have been

• reaction components maximises the yield of 7a (Table 1, runs 3–6). These results very strongly suggest unprecedented anionic [3,3]-sigmatropic rearrangement starting from 1d; another addition to the body of evidence for the importance of charge upon sigmatropic rearrangements [25][26]. In the subsequent