Formation of azetidines by electrophilic cyclizations have been reported, starting with homoallylic amines (4-exo mode cyclizations). We reported that the formation of these compounds can be carried out starting with allylic amines (4-endo mode cyclizations) using bis(collidine)bromonium(I) hexafluorophosphate as an electrophile. These cyclizations occur via a carbocation intermediate.
(2-Bromoethyl)sulfonium Trifluoromethanesulfonates in Stereoselective Annulation Reactions for the Formation of Fused Bicyclic Epoxides and Aziridines
作者:Sven P. Fritz、Zulfiquar Ali、Matthew G. Unthank、Eoghan M. McGarrigle、Varinder K. Aggarwal
DOI:10.1002/hlca.201200455
日期:2012.12
A versatile and simple method is reported for the synthesis of bicyclic epoxide and aziridinefused heterocycles (up to 98% yield, up to 96 : 4 er or up to 15 : 1 dr), using a tandem Michaeladdition/JohnsonCoreyChaykovsky annulation approach. A new chiral (2‐bromoethyl)sulfonium reagent is described, based on an easily available chiral sulfide; it promotes or enhances stereoselectivity in the reaction
Stereochemical aspects of high-pressure [4+2] cycloaddition between 1-methoxybuta-1,3-diene and N-protected α-amino aldehydes are discussed. In addition, the zinc bromide catalyzed cyclocondensation of 1-ethoxy-3-silyloxybuta-1,3-diene and N-protected α-amino aldehydes is studied, at ambient pressure.