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Synthesis of (−)-Sedinine by Allene Cyclization and Iminium Ion Chemistry
journal contribution
posted on 2010-09-03, 00:00 authored by Roderick W. Bates, Yongna LuA synthesis of the sedum alkaloid sedinine has been achieved employing silver(I)-catalyzed allenic hydroxylamine cyclization and ring-closing metathesis to form a bicyclic N,O-acetal. Ring opening of this acetal with a silyl enol ether under Lewis acidic conditions is exclusively trans selective, leading to the natural product after reduction. On the other hand, conversion of the bicyclic N,O-acetal to a semicyclic N,O-acetal results in no stereoselectivity during such a reaction. The contrasting results can be rationalized by consideration of the conformation of the iminium ions.