Tandem reactions via Barton esters with intermolecular addition and vinyl radical substitution onto indole

A one-pot initiator-free Barton ester decomposition with tandem radical addition onto alkyl propiolates or phenylacetylene with aromatic substitution of the resultant vinyl radical allows convenient access to new 9-substituted 6,7-dihydropyrido[1,2-a]indoles. Propyl radical cyclizations compete when forming the expanded 7,8-dihydro-6H-azepino[1,2-a]indole system. 2-Thiopyridinyl S-radical is incorporated into aromatic adducts when using unsubstituted indole-1-alkanoic acid precursors. X-ray crystallography on substitution products allows selectivity of the radical addition onto less reactive internal alkynes to be determined.