Yttrium-Catalyzed Addition of Benzylic C—H Bonds of Alkyl Pyridines to Olefins

摘要

It is well-known that the benzylic C-H bonds of α-alkyl pyridines react with electrophiles to form C—C bonds in a nucleophilic fashion. However, the substrate scope reported so far for this transformation is mostly limited to highly reactive polar electrophiles, such as halides,12 car-bonyl groups, imines, and enones. Reactions of simple olefins with the benzylic C—H bonds of alkyl pyridines remain scarce. In particular, the catalytic addition of the benzylic C-H bond of alkyl pyridines to a simple olefin has not been reported previously. Therefore, the search for new catalysts for this reaction is of much interest and importance because it would provide a useful protocol for the efficient synthesis of various alkylated pyridine derivatives, which are important structural motifs often found in natural products, pharmaceuticals, ligands, and functional materials. We report herein that cationic half-sandwich yttrium alkyl complexes can catalyze the addition of benzylic C-H bonds of various 2,6-dialkyl-substituted pyridines to a variety of olefins such as ethylene, 1-hexene, styrenes, and 1,3-conjugated dienes, to afford new alkylated and allylated pyridine derivatives.