A convenient synthesis of 8‐substituted indolizines as precursors to 5‐substituted cycl{3.2.2}azine derivatives

The synthesis of 8‐substituted indolizines is described via a two step process in which a 1,4‐diketone, containing a rerf‐butyl group, is cyclocondensed with a trialkylsilyl protected pyrrole to provide 5,8‐disubstituted indolizines in higher yields than the identical reaction with unprotected pyrrole. Cleavage of the tert ‐butyl group from the indolizine 5‐position, by treatment with 85% phosphoric acid, provides 8‐substituted indolizines in good yields. Treatment of 8‐substituted indolizines with dimethyl acetylenedicarboxylate, in the presence of palladium‐on‐carbon, provides novel 5‐substituted cycl{3.2.2) derivatives.