One-Pot Generation and Conversion of Trichloroacetimidates for the Racemization-Free Allylation and Benzylation of α-Hydroxyesters and the Enantiopure Synthesis of a Chiral Diglycole
摘要:
O-Allylations and O-benzylations of alpha -hydroxy esters (3a-3c) are performed without racemization. The reagents applied, O-allyl- and O-benzyltrichloroacetimidate (5a, 5b) are prepared and converted in a one-pot-procedure. After protection by benzylation (S)-(-)-ethyl lactate (3a) is converted by a sequence of carbonyl reduction, alcohol activation, ether formation, and deprotection to the optically active diglycole derivative 1a.
Intramolecular 1,3-Dipolar Cycloaddition of Transient Enantiomerically Pure Oxaalkenyl Nitrones
作者:Hans Günter Aurich、Frank Biesemeier
DOI:10.1055/s-1995-4060
日期:1995.9
A variety of enantiomerically pure α-hydroxy esters were converted into enantiomerically pure 3,7-dioxa-2-azabicyclo[3.3.0]octanes 7 by the following reaction sequence. Allylation of the hydroxy group was followed by reduction of the ester group. The resulting aldehyde was treated with an N-alkylhydroxylamine to give an oxaalkenyl nitrone 6 which underwent spontaneously an intramolecular 1,3-dipolar cycloaddition affording 7. Opening of the isoxazolidine ring of 7 by various reductive methods yielded the highly substituted tetrahydrofuran derivatives 11.
Stereoselective intramolecular cycloadditions of homochiral nitrilimines: synthesis of enantiopure (6S)-substituted-2,3,3a,4,5,6-hexahydro-furo[3,4-c]pyrazoles
作者:Lara De Benassuti、Luisa Garanti、Giorgio Molteni
DOI:10.1016/j.tetasy.2004.02.002
日期:2004.4
Starting from (S)-ethyl lactate and (S)-ethyl mandelate the homochiral hydrazonoyl chlorides 4b-d have been synthesised. Their base treatment promoted the in situ generation of the corresponding nitrilimines 5b-d, which gave the enantiopure title compounds with good overall yields and diastereoselectivities. (C) 2004 Elsevier Ltd. All rights reserved.
Aurich, Hans Guenther; Biesemeier, Frank; Boutahar, Mostafa, Chemische Berichte, 1991, vol. 124, # 10, p. 2329 - 2334
作者:Aurich, Hans Guenther、Biesemeier, Frank、Boutahar, Mostafa
DOI:——
日期:——
One-Pot Generation and Conversion of Trichloroacetimidates for the Racemization-Free Allylation and Benzylation of α-Hydroxyesters and the Enantiopure Synthesis of a Chiral Diglycole
O-Allylations and O-benzylations of alpha -hydroxy esters (3a-3c) are performed without racemization. The reagents applied, O-allyl- and O-benzyltrichloroacetimidate (5a, 5b) are prepared and converted in a one-pot-procedure. After protection by benzylation (S)-(-)-ethyl lactate (3a) is converted by a sequence of carbonyl reduction, alcohol activation, ether formation, and deprotection to the optically active diglycole derivative 1a.