Synthesis of Functionalized Olefins by Cross and Ring-Closing Metatheses

Abstract

The generation of olefins with electron-withdrawing functionality, such as α,β-unsaturated aldehydes, ketones, and esters, remains a difficult task in organic chemistry. A practical method to approach this problem would involve olefin metathesis, utilizing well-defined alkylidenes such as ((CF_3)_2MeCO)_2(ArN)Mo CH(t-Bu) (1) and (Pcy_3)_2Cl_2Ru CHPh (2). However, the generation of olefins with vinylic functionality through the use of cross-metathesis (CM) has met with limited success. In one of the few reports of this reaction, Crowe and Goldberg demonstrated that acrylonitrile participated in cross-metathesis reactions with a variety of terminal olefins. Other π-conjugated olefins, such as enones and enoic esters, were not functional group compatible with alkylidene 1 and failed to react with 2 in cross-metathesis. Recently, the highly active ruthenium-based olefin metathesis catalyst 3, which contains a 1,3-dimesityl-4,5-dihydro-imidazol-2-ylidene ligand, was found to efficiently catalyze the cross-metathesis of 1,1-geminally disubstituted olefins.7 Because ruthenium alkylidene 3 displayed unique activity toward previously metathesis-inactive substrates, we decided to investigate the metathesis of α-functionalized olefins. In this communication, we report the single-step synthesis of α-functionalized olefins by intermolecular cross-metathesis and intramolecular ring-closing metathesis using ruthenium alkylidene 3.