Metal-dependent modulation of diastereoselectivity in the Barbier-type crotylation of (R)-cyclohexylideneglyceraldehyde
摘要:
The diastereoselectivity of the Barbier-type crotylation of (R)-cyclohexylideneglyceraldehyde could be tuned by changing the metal atom and solvent. The Ga-mediated reaction in [bmim][Br] produced the best diastereoselectivity, furnishing the all-anti product in good yield. (C) 2009 Elsevier Ltd. All rights reserved.
The Barbier‐type allylation of aldehydes and ketones can be carried out with both unsubstituted and γ‐substituted allyl bromides using only a catalytic amount (0.1 equiv.) of In metal in [bmim][Br].
syn-Selective crotylation of aldehydes using bismuth-crotyl bromide-(1-butyl-3-methylimidazolium bromide) combination: some synthetic applications
作者:Dibakar Goswami、Mrunesh R. Koli、Sucheta Chatterjee、Subrata Chattopadhyay、Anubha Sharma
DOI:10.1039/c7ob00626h
日期:——
The Bi-[bmim][Br] combination has been found to offer high syn-selectivity in the crotylation of aldehydes with crotylbromide using practically stoichiometric amounts of the reagents. The room temperature ionic liquid (RTIL), [bmim][Br], activated Bi metal in the presence of oxygen to produce crotylbismuthdibromide, which reacted with the aldehydes at room temperature. The major anti–syn diastereomeric
An efficient synthesis of (-)-prelactone B has been developed using 1,2-cyclohexylidene glyceraldehyde as the chiral template. The key features of the synthesis were stereoselective crotylation of 1,2-cyclohexylidene glyceraldehyde and enantioselective reduction of a ketone, as well as operational simplicity and use of inexpensive reagents/chemicals.
A facile asymmetric synthesis of the octalactinlactone was developed staring from (R)-cyclohexylideneglyceraldehyde (1). The key step of the synthesis is an In-mediated diastereoselective crotylation of 1 in water, which furnished the building blocks with the required stereochemistry under operationally simple conditions. Their conversion to the appropriate intermediates, invertive esterification
a representative example of chiral β,γ-disubstituted-γ-butyrolactones. In this endeavor, crotylations of 1 in THF mediated with four low valent metals were studied. All these reactions took place efficiently producing 2 in good yields but with varied stereoselectivities. Each reaction produced the corresponding secondary alcohol adduct 2b and 2c predominantly with diastereoisomer 2a only in trace amounts