Modular Access to Bifunctional Norbornenes and Their Application in Ring-Opening Metathesis Polymerization

A variety of exo-2,3-bifunctional norbornenes were prepared by the formal addition of C(aryl)-COCl bonds across norbornadiene using a palladium catalyst. The resulting exo-2,3-disubstituted norbornenes feature an aryl group and an acid chloride. Here, we trap the acid chloride in situ to prepare norbornenes with a methyl ester, a pentafluorophenyl ester, a sterically hindered secondary amide, and an N-methyl-N-methox-yamide (Weinreb amide). This modular strategy enabled the expedient preparation of a set of bifunctional monomers which were subjected to ring-opening metathesis polymerization with Grubbs first-generation catalyst. We show that the polymerization is compatible with a variety of aryl substituents including an azobenzene, a protected terminal alkyne, a boronic ester, and a furan. In addition, three monomers are subjected to polymerization at different M/I ratios and were found to give a near-linear increase in molecular weight. Furthermore, living polymerization was demonstrated by the successful preparation of block copolymers.