selective dehydrohalogenation to form alpha-haloacrylate analogues. A variety of alpha-halo Michael acceptors were prepared in dimethyl sulfoxide under mild, base-free conditions, including the preparation of alpha-bromoacrolein and alpha-chloro- and bromoacrylonitriles. Synthesis of these molecules has been reported in the literature to be difficult. Among all the existing dehydrohalogenation procedures
using n-Bu4NBr afforded 2-cyano-2-siloxyvinylallenes via a tandem process that involves a nucleophilic attack of a cyanide ion and a Brookrearrangement induced conjugate vinylic 1,4-elimination. Use of a chiral cyanide ion source, derived from KCN and quaternary ammonium bromide derived from cinchona alkaloids, provided nonracemic allene derivatives. Based on this result and the reaction using a chiral
Enantioselective preparation of a C3 symmetrical triol
作者:Henning Lütjens、Paul Knochel
DOI:10.1016/0957-4166(94)80146-0
日期:1994.7
The new C3 symmetrical triol 1 has been prepared in optically pure form (98 %ee) using a catalytic enantioselective ethylation of a functionalized unsaturated aldehyde in an iterative way and a diastereoselectivehydroboration.
NHC-Catalyzed [3 + 3] Annulation of Thioamides and Modified Enals for the Enantioselective Synthesis of Functionalized Thiazinones
作者:Arghya Ghosh、Soumen Barik、Akkattu T. Biju
DOI:10.1021/acs.orglett.9b03188
日期:2019.11.1
(NHC)-catalyzed [3 + 3] annulation of thioamides with modified enals allowing the enantioselective synthesis of functionalized 1,3-thiazin-4-ones is reported. The NHC generated from the chiral triazolium salt was optimal and the reaction is initiated by the thia-Michael addition to catalytically generated α,β-unsaturated acylazolium intermediates derived from 2-bromoenals, followed by intramolecular cyclization
The scope of the three-component reaction of aldehydes, amides, and dienophiles, the so-called AAD reaction, is extended to the formation of 2- and 3-bromo-substituted 1-amido-2-cyclohexene derivatives. The incorporation of the halogen substituent allows further elaboration of this interesting class of products.