Enantioselective, Cyclopentene-Forming Annulations via NHC-Catalyzed Benzoin−Oxy-Cope Reactions

Abstract

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Five‐Membered Heterocycles with Three Heteroatoms: Triazoles

“…Chiral catalyst 245 promoted the intramolecular Stetter cyclization of an aldehyde onto a vinylphosphine oxide or vinylphosphonate Michael acceptor [289]. Chiral triazolium salt 246 has been employed successfully in the hetero Diels-Alder reactions of a-chloroaldehyde bisulfite adducts with various oxodienes under biphasic reaction conditions with high levels of enantioselectivity [290] and in the highly enantioselective cis-cyclopentene-forming annulation reactions [291]. Bicyclic 1,2,4-triazolium salts have varied synthetic utility in a host of reactions.…”

Chiral N-heterocyclic carbene-catalyzed generation of ester enolate equivalents from α,β-unsaturated aldehydes for enantioselective Diels–Alder reactions

“…These species have long been known to act as nucleophiles in reactions with a range of electrophilic partners including aldehydes, electron-deficient olefins (Stetter reactions) (4), imines (5), and oxidants (6, 7). As we and Glorius first demonstrated in 2004 (8,9), the use of α,β-unsaturated aldehydes and suitable catalysts makes possible the catalytic generation of homoenolate equivalents for the synthesis of γ-lactones, γ-lactams (10, 11), cyclopentenes (12,13), and numerous catalytic cascades (14,15) often with high levels of enantioselectivity.…”

“…Although this has proven possible in carefully designed intramolecular systems, such as those reported by Scheidt and co-workers (31), the use of simple α,β-unsaturated aldehydes as ester enolate precursors has not been achieved. Attempts to date have resulted in dramatically different reactivity as the homoenolate pathway dominates (Scheme 1) (12,13). This can be exploited for highly enantioselective cascade reactions but not for the desirable intermolecular reactions of catalytically generated ester enolate equivalents.…”

Progress of Cooperative Catalysis in Organic Synthesis

“…将在一定条件下可兼容的不同类型 有机催化剂进行"组合", 通过有机-有机共催化模式来 提高合成效率已成为催化领域的又一研究方向. [29,30] . 同时, 邻氯苯甲酸通过氢键作用活化不 饱和亚胺 51, 两个被活化的反应物通过类 aldol 缩合反 应及串联的环化反应得到 γ-内酰胺 54 [31] .…”