Some indolizine derivatives having (2-cyanoethyl)thio or (2-ethoxycarbonylethyl)thio group at the 2-position were prepared in moderate to good yields starting from the corresponding pyridinium 1-(thiocarbonyl)methylides. The treatment of these indolizines with a strong base such as potassium t-butoxide in N,N-dimethylformamide (DMF) gave smoothly title compounds, 2-indolizinethiols, with the elimination
title compounds, thieno[3,2-a]- and thieno[2,3-b]indolizine derivatives were obtained in fairly good yields. The cyclization modes observed in these transformation reactions were in accord with those expected by the molecular orbital calculations using some model compounds and by the stereochemical consideration of starting indolizines. The alkylations of 3-hydroxythieno[3,2-a]- and 3-hydroxythieno[2