Experimental study of organocatalyzed homodimerization reactions of alpha,beta-unsaturated enones.

摘要

This Thesis intends to elucidate the mechanism involved in a self condensation (Homodimerization) transformation of alpha, beta-unsaturated ketones through the formation of a key enamine intermediate that arises as a consequence of the presence of an organocatalyst. The organocatyst utilized in this research is L-Proline, a natural occurring aminoacid. While the mechanism of the L-Proline organocatalyzed self-condensation reaction of alpha, beta-unsaturated enals appears to proceed through an imine addition mechanism (Double Michael Addition), the analogous reaction pathway for Homodimerization of alpha, beta-unsaturated enones has been postulated to proceed via a Diels-Alder reaction.;This Thesis work is significant as the elucidation of the mechanism followed by the Homodimerization transformation, Double Michael Addition or a Diels-Alder Cyclization, will make a contribution to the present understanding on enamine-iminium catalysis, and it will aid in predicting and rationalizing the stereochemistry observed for the reaction products in related organocatalyzed transformations. The chemistry performed in this Thesis work involves neat, room temperature reaction conditions and easy recycling of the catalyst. Consequently, this Thesis is also contributing to the design of Green Chemistry methodologies. This Thesis intends to determine whether an L-Proline organocatalyzed self-condensation reaction of 2-Cyclohexenone with Pyrrolidine or L-Methylprolinate would proceed by an imine addition Double Michael mechanism or a Deis-Alder Homodimerization pathway. While we now show that the Endo homodimer is indeed the major product of this organocatalytic reaction we have also isolated some unusual side products that implicate a Diels-Alder reaction mechanism. The elucidation of the mechanistic pathway for these transformations will add insight to the research on organocatalysis through enamine/iminium formation using aminoacids as organocatalysts, and to advance the field of green chemistry and its potential applications.