C9-stereochemistries. A new radical-based strategy was devised to construct the pentacyclic skeletons of 1 and 2. An oxacycle-fused A-ring and enyne fragments were coupled to produce radical precursors 4a–4c with different C7-oxygen functionalities. The bridgehead tertiary bromide of 4a–4c participated in a radical cascade reaction with the three unsaturated bonds to cyclize the C9-diastereomeric BCD-rings.
Cascade radical cyclisations leading to steroid ring constructions. Regio- and stereo-chemical studies using ester- and fluoro-alkene substituted polyene acyl radical intermediates
作者:Haydn M. Boehm、Sandeep Handa、Gerald Pattenden、Lee Roberts、Alexander J. Blake、Wan-Sheung Li
DOI:10.1039/b002999h
日期:——
the E-substituted diene selenyl ester 7 underwent sequential cyclisations in the presence of Bu3SnH-AIBN leading to the trans-decalone 8 exclusively, the corresponding Z- and E-isomers of the methoxycarbonyl-substituted diene 16, under similar conditions, gave rise to a 2∶1 mixture of the trans- and cis-decalones 17a and 17b respectively in 62–73% yield. Cyclisation of the triene selenoate 30 led to
azacycles by a biomimetic cascade cyclization of arylalkenyl dioxazolones. This cascade reaction was found to proceed with excellent stereoselectivity and a high functional group tolerance. The substrate scope of arylalkenyl dioxazolones turned out to be highly flexible and extendable to additional terminating subunits, such as heteroaryl and alkynyl moieties. This biomimeticcyclization was elucidated