Enantioselective All-Carbon (4+2) Annulation by <i>N</i>-Heterocyclic Carbene Catalysis
作者:Lisa Candish、Alison Levens、David W. Lupton
DOI:10.1021/ja508542n
日期:2014.10.15
The enantioselective vinylogous Michael/aldol cascade is an underdeveloped approach to cyclohexenes. Herein we describe a highly enantioselective (most >= 98:2 er) and diastereoselective (all >= 15:1 dr) N-heterocyclic carbene catalyzed cycloisomerization of acyclic dienyl esters to cyclohexyl beta-lactones. Derivatizations avail cyclohexenes bearing four contiguous stereogenic centers, while mechanistic studies support olefin isomerization prior to cyclization.
Knoevenagel Adducts from Reactions between Glutaconate Moieties and Aldehydes and Their Adducts with Primary Amines and Enamines
2-dihydropyridines such as 26 or 27. Diene 21 was also shown to give diastereoisomeric cycloadducts 30 or 32 with enamines or oxazolidine derivatives. The cycloadducts 30 were finally shown to react with n-butylamine in acidicmedium to give rearranged cyclopentenes 36 and 37. Although the synthesis of derivatives such as 9 or 10, corresponding to the AB ring system of manzamine A, by this approach have yet