Gold-catalyzed deoxygenative nazarov cyclization of 2,4-dien-1-als for stereoselective synthesis of highly substituted cyclopentenes.
Treatment of 2,4-dien-1-als with allylsilanes and PPh(3)AuSbF(6) (3 mol %) led to formation of 1,4-bis(allyl)cyclopentenyl products; this gold catalyst is superior to commonly used Lewis acids according to catalyst screening. Such gold-catalyzed deoxygenative cyclizations are compatible with various oxygen-, amine-, sulfur-, hydrogen-, and carbon-based nucleophiles. The value of this new catalysis is demonstrated by the diverse annulations of 2,4-dien-1-als with electron-rich alkenes and arenes, providing an easy access to complicated cyclopentenyl frameworks. Structural analysis of annulation products reveals evidence for the participation of Nazarov cyclization. This deoxygenative cyclization is extensible to a tandem intramolecular cyclization/nucleophilic addition cascade, giving polycyclic carbo- or oxacyclic compounds with controlled stereochemistry. This new gold catalysis is applied to a short synthesis of natural compounds of the brazilane family, including brazilane, O-trimethyl-, and O-tetramethyl brazilane.
Lin
Chung-Chang
CC
Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan, ROC.
Teng
Tse-Min
TM
Tsai
Chung-Chih
CC
Liao
Hsin-Yi
HY
Liu
Rai-Shung
RS