Sequential aza-Baylis-Hillman/Ring closing metathesis/aromatization as a novel route for the synthesis of substituted pyrroles

A new route to diverse 2-substituted-3-methoxycarbonyl pyrroles has been developed. Diverse SES protected R-methylene-aminoesters were obtained by a 3-component aza-Baylis-Hillman reaction. Diversity arose from the aryl aldehydes which can be used in this reaction. N-Alkylation with allyl bromide under mild conditions provided the corresponding dienes. These substituted dienes were cyclized by ring closing metathesis at room temperature or under microwave-activation with Grubbstype II catalyst to yield SES-protected pyrroline intermediates. The final pyrroles were obtained by base-promoted dehydrodesulfinylation/aromatization. The scope of each of these reactions was explored