Configurationally stable biaryl analogues of 4-(dimethylamino)pyridine: A novel class of chiral nucleophilic catalysts

A short synthetic approach toward a novel class of chiral nucleophilic cata lysts, the dissymmetry of which stems from restricted rotation about an Ar- Ar bond, has been developed. The key steps of the synthesis include prepara tion of a nucleophilic 1-methyl-2-pyrrolino[3,2-c]pyridine core 16 by ortho -lithiation and creation of the biaryl axes via Suzuki cross-coupling react ions. Comparative HPLC studies of racemization for configurationally labile biaryls 31, 38, and 43 containing 1-methyl-2-pyrrolino[3,2-c]pyridine, 4-( dimethylamino)pyridine, and 4-(1-pyrrolidino)pyridine cores, respectively, have demonstrated that a pyrrolidino substituent ortho to the biaryl axis i s optimal for slowing Ar-Ar rotation. Biaryls containing all three cores ha ve been shown to retain DMAP-like catalytic activity in the acylation of a hindered alcohol. Biaryls 55 and 56, which are configurationally stable at ambient temperature, have also been prepared via modification of configurat ionally labile derivatives. Compounds 55 and 56 in optically pure form shou ld provide a useful starting point for studies on catalytic asymmetric acyl transfer using atropisomeric analogues of DMAP.