Rhodium(I)-catalysed alkylation of 2-vinylpyridines with alkenes as a result of C–H bond activation

Abstract

2-Vinylpyridines undergo regioselective β-alkylation with alkenes in the presence of a rhodium(I) complex as a catalyst to give products resulting from an anti-Markownikoff reaction. These results show the feasibility of alkylation of an alkenic position as a result of C–H bond activation. 2-(Prop-1-en-2-yl)pyridine 1 and 1-phenyl-1-(2-pyridyl)ethylene 15 react with linear terminal alkenes to give the corresponding alkylated products in high yields. Cyclic alkenes, allyl alcohol, but-3-en-1-ol and methyl vinyl ketone, however, fail to react with 1. Pent-2-ene gives the linear alkylated product in low yield. 6-Methyl-2-vinylpyridine 24 and 2-vinylpyridine 32 give the alkylated products in low yield together with their dimeric products. The alkenic C–H bond of 2-(cyclohex-1-enyl)pyridine 36 has been regioselectively alkylated. 2-(Cyclohex-1-enyl)pyridine 36 with alkenes in the presence of the Rh^I catalyst undergoes regiospecific alkylation at the alkenic position.