Homochiral 4-hydroxy-5-hexenoic acids and their derivatives and homologues from carbohydrates
摘要:
Efficient routes to chiral 4-hydroxy-5-hexenoic acids and lactones from D-gluconic acid-delta -lactone and L-mannonic acid-gamma -lactone are described. In this approach, the starting lactones are converted to 2,6-dibromo compounds that readily undergo zinc mediated elimination to generate the terminal alkene group in concert with 2-deoxygenation. The integrity of the remaining stereocenters is preserved during the reaction. The related important pharmaceutical intermediates (S)-3-hydroxy-4-pentenoic acid and (S)-1.3-dihydroxy-4-pentene were also prepared from 2-deoxyribose via the corresponding aldonolactone. (C) 2001 Elsevier Science Ltd. All rights reserved.
Ring-Closing Metathesis Reactions of Acyloxysulfones: Synthesis of γ-Alkylidene Butenolides
作者:Gregory O’Neil、Iris Phan、Garrett Gilbert
DOI:10.1055/s-0034-1378721
日期:——
An acyloxysulfone ring-closing metathesis/sulfone elimination sequence has been developed for the preparation of various γ-alkylidenebutenolides. The elimination is proposed to proceed via an E1cb mechanism leading to (Z)-γ-alkylidene butenolides as the major products.
Virtually perfect transmittal of the enolate reactivity up to five conjugated double bonds from the origin allows a series of furan-based silyloxypolyenes to add to aldehyde carbonyls at the most distant point of the molecule. Denmark’s axially chiral bisphosphoramide/SiCl4 combination catalyzes these scantly precedented, long-range Mukaiyama-type vinylogous aldol reactions efficiently, providing a palette