Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• trimethyl orthoacetate the enantiomerically pure bromomethoxy derivative (4R,5R)-37 was prepared after crystallization of the reaction mixture. The precursor of the carboxymethyl group was first introduced with full retention of configuration employing a stannate chemistry to give (4R,5R)-38 after removal

Total synthesis of a Streptococcus pneumoniae serotype 12F CPS repeating unit hexasaccharide

• Peter H. Seeberger,
• Claney L. Pereira and
• Subramanian Govindan

Beilstein J. Org. Chem. 2017, 13, 164–173, doi:10.3762/bjoc.13.19

• obtain 35, required several protecting group manipulation steps: cleavage of the two acetate esters of 31 to produce diol 32 was followed by the reaction with trimethyl orthoacetate to provide the ortho-ester 33, which was regioselectively opened under acidic conditions to afford disaccharide acceptor 34

• . Reagents and conditions: (a) TMSOTf, CH2Cl2, −30 °C, 74%; (b) NaOMe (0.5 M in MeOH), MeOH, rt; (c) trimethyl orthoacetate, p-TsOH, toluene; (d) 80% AcOH, rt, 71% over three steps; (e) 9, NIS, TMSOTf, dioxane/toluene (3:1), −10 °C, 54%; (f) HF-pyridine, THF, 0 °C; (g) CCl3CN, DBU, CH2Cl2, 0 °C, 57% over two

• :1), rt, 90%; (f) i. TEMPO, BAIB, CH2Cl2/H2O (4:1), rt; ii. MeI, K2CO3, DMF, rt, 35% over two steps; (g) 8, TMSOTf, CH2Cl2, −20 °C, 77%; (h) i. NaOMe (0.5 M in MeOH), THF/MeOH (1:1); ii. trimethyl orthoacetate, p-TsOH, toluene; iii. 80% AcOH, rt, 27% over three steps; (i) 9, NIS, TMSOTf, dioxane

Synthesis and in vitro cytotoxicity of acetylated 3-fluoro, 4-fluoro and 3,4-difluoro analogs of D-glucosamine and D-galactosamine

• Štěpán Horník,
• Lucie Červenková Šťastná,
• Petra Cuřínová,
• Jan Sýkora,
• Kateřina Káňová,
• Roman Hrstka,
• Ivana Císařová,
• Martin Dračínský and
• Jindřich Karban

Beilstein J. Org. Chem. 2016, 12, 750–759, doi:10.3762/bjoc.12.75

• of the benzoyl group and a subsequent reaction of the salt 24 with methanol upon quenching. A similar participation of a vicinal O-acetyl protecting group on reaction with DAST leading to the formation of an orthoacetate was reported [47]. Reaction of fluorohydrin 20 with DAST proceeded with

The synthesis of active pharmaceutical ingredients (APIs) using continuous flow chemistry

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2015, 11, 1194–1219, doi:10.3762/bjoc.11.134

• as a potential way of circumventing these specific problems and so was extensively investigated. The developed flow route [71] started with the reaction of methyl dichlorophosphine (66) and triethyl orthoacetate (67), which in batch could only be performed under careful addition of the reagent and

Convergent synthesis of a tetrasaccharide repeating unit of the O-specific polysaccharide from the cell wall lipopolysaccharide of Azospirillum brasilense strain Sp7

• Pintu Kumar Mandal,
• Debashis Dhara and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2014, 10, 293–299, doi:10.3762/bjoc.10.26

• mmol) in dry DMF (10 mL) was added triethyl orthoacetate (5.5 mL, 30.03 mmol) followed by p-TsOH (100 mg), and the reaction mixture was allowed to stir at room temperature for 2 h. The reaction mixture was concentrated under reduced pressure, and a solution of the crude product in 80% aq AcOH (80 mL

• % aq AcOH, 80 °C, 1.5 h, 72% overall yield; (d) triethyl orthoacetate, p-TsOH, DMF, 2 h then 80% aq AcOH, room temperature, 1 h, 74%. Reagents: (a) N-iodosuccinimide (NIS), TfOH, CH2Cl2, MS 4 Å, −30 °C, 1 h, then 0 °C, 1 h, 77%; (b) NIS, TfOH, CH2Cl2/Et2O 1:1, MS 4 Å, −25 °C, 30 min, 75%; (c) NIS, TfOH

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• signature oxetane moiety. Ether cleavage [144] and Swern oxidation resulted in the formation of ketone 169. HWE-olefination followed by reduction to the allyl alcohol led to allylic ester 170 after a Johnson–Claisen rearrangement [145] upon treatment with triethyl orthoacetate. Ester 170 was saponificated

Approaches to α-amino acids via rearrangement to electron-deficient nitrogen: Beckmann and Hofmann rearrangements of appropriate carboxyl-protected substrates

• Sosale Chandrasekhar and
• V. Mohana Rao

Beilstein J. Org. Chem. 2012, 8, 1393–1399, doi:10.3762/bjoc.8.161

• ), their carboxyl groups being masked as a 2,4,10-trioxaadamantane unit (an orthoacetate). The oxime mesylates have been rearranged with basic Al2O3 in refluxing CHCl3, and the malonamic acids with phenyliodoso acetate and KOH/MeOH. Both routes are characterized by excellent overall yields. Structure

• rearrangement; orthoacetate; trioxaadamantane; Introduction The synthesis of α-amino acids remains of continuing interest for at least two reasons: Firstly, obtaining a particular amino acid via protein hydrolysis implies its separation from other amino acids (and their possible wastage, particularly on large

Approaches towards the synthesis of 5-aminopyrazoles

• Ranjana Aggarwal,
• Vinod Kumar,
• Rajiv Kumar and
• Shiv P. Singh

Beilstein J. Org. Chem. 2011, 7, 179–197, doi:10.3762/bjoc.7.25

• triethyl orthoacetate in acetic anhydride whilst methoxyarylmethylidenemalonitriles 101b,c were obtained via a two step procedure involving the aroylation of the malonitrile with aroyl chlorides in the presence of NaH, followed by the treatment of the resulting intermediate with dimethyl sulfate. Nilov et

Convergent syntheses of Le^X analogues

• An Wang,
• Jenifer Hendel and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2010, 6, No. 17, doi:10.3762/bjoc.6.17

• ] (Scheme 2). Diol 20 was first acetylated to the diacetate 21 which was then treated with 90% AcOH at 70 °C to remove the isopropylidene group affording diol 22. The diol 22 was selectively acetylated at O-4 by converting it to the corresponding cyclic methylorthoacetate and opening the orthoacetate in

Investigation of acetyl migrations in furanosides

• O. P. Chevallier and
• M. E. Migaud

Beilstein J. Org. Chem. 2006, 2, No. 14, doi:10.1186/1860-5397-2-14

• conformation) can form easily under mildly basic or acidic conditions. In riboside 3, the rigid conformation of the furanose ring prevents the formation of this orthoacetate. Similarly, no migration product 4b (Table 4) was detected when arabinoside 4 was treated with TBAF in THF while as expected, the acetyl

• trans-esterification occurrence. Unfortunately, the formation of a six-membered ring orthoacetate appears to be facilitated under acid-catalysed reaction conditions and total intramolecular acetyl migration occurred in xyloside 2 in the presence of CAN, showing how finally balanced things are in these

• systems. In conclusion, to minimise acetyl migration in furanoside derivatives, base-catalysed reactions should be conducted under dilute conditions when the formation of an orthoacetate is disfavoured to minimise intermolecular transesterification. Unfortunately, we have been unable to identify a set of