Stereocontrolled Synthesis of Exocyclic Trisubstituted Double Bonds by Stereospecific Iminium Ion-Vinylsilane Cyclizations. A Short Synthetic Route to Indoloquinolizidine Alkaloids

Article abstract of DOI:10.1021/jo00148a013

The reaction of (Z)- and (E)-trisubstituted vinylsilanes 9 and 10 with paraformaldehyde and acid proceeded with >98percent retention of configuration to give indoloquinolizidines 13 and 3 in excellent yield.This is the first demonstration that iminium ion-vinylsilane cyclizations occur with complete retention of configuration with either vinylsilane stereoisomer.The simple indole alkaloid dl-deplancheine (3) was prepared in a stereocontrolled fashion in 26percent overall yield from commercially available 1-(trimethylsilyl)propyne.