Addition reactions of allyl stannanes to an indolo[2′,3′:3,4]pyrido[1,2-b]isoquinoline imminium salt

The addition of organometallic reagents to the 13b-position of the indolo[2',3':3,4]pyrido[1,2-b]isoquinoline imminium salt 4 is described. Reaction of 4 with tetraallyl tin in 2-methoxyethanol gave the allyl adduct 7 in moderate yield. Further elaboration of 7 yielded the pentacyclic benzylidene alcohols 13 and 14. Structure elucidation of the compounds prepared was achieved by a combination of H-1 nmr spectroscopy and X-ray crystallography.