[GRAPHICS]The PdCl2-catalyzed cyclization of alpha-alkoxy dienones leads to 2-hydroxycyclopentenones, whereas the Pd(OAc)(2)-catalyzed reaction leads to cross-conjugated cyclopentenones through an oxidative process.
Tandem alkylation–cyclization process via an O,C-dianion
摘要:
A general protocol for preparing densely functionalized cyclopentenones through a tandem nucleophilic addition-deprotonation-alkylation-cyclization process is described. Addition of lithioallene 2 to enamides 1 generates tetrahedral intermediate 3. Deprotonation of the gamma carbon atom of the allene function in situ, followed by trapping by a suitable electrophile and cyclization during workup leads to C6 substituted cyclopentenones 6. (c) 2005 Elsevier Ltd. All rights reserved.
作者:Paul E. Harrington、Tsuyoshi Murai、Chester Chu、Marcus A. Tius
DOI:10.1021/ja020591o
日期:2002.8.1
The scope of an enantioselective cyclopentannelation reaction that makes use of allenyl ether-derived nucleophiles has been probed. The enantioselectivity is induced by a traceless chiral auxiliary that is easily derived from camphor. It has been shown that for gamma-substituted allene ethers that are axially chiral, very high enantiomeric excesses of cyclopentenone products are observed in the matched cases. Two fundamentally different mechanisms are observed, one for the cyclizations of allenyl ketones (see eq 7), the other for the cyclizations of allenyl alcohols (see eq 11). The methodology is versatile, efficient, and well-suited for applications in synthesis.