Functionalized enamines—XVII : Ring expansion of α,β-unsaturated cyclic ketones by reaction of pyrrolidine dienamines with dihalocarbenes; Synthesis of A-homo-steroids

Reaction of pyrrolidine dienamine 2b with carbenes 3a and 3b leads to the formation of ring expanded ketones 4a and a mixture of 4a and 4b, respectively. The ring-expansion reaction has been utilized in a two-step conversion of Δ⁴-cholestenone and testoterone acetate into the A-homo-steroids 7a-c. Structure assignments and the mechanism of formation of the reaction products are discussed.