Ketones methylenation using Tebbe reagent

A few years later, Tebbe and co-workers found that the methylene-bridged metallacycle 3, which has become known as the Tebbe reagent, is useful for the methylenation of ketones and aldehydes [5]. Titanocene-methylidene 4, the active species of this olefination, also transforms carboxylic acid derivatives into heteroatom-substituted olefins. Because the carbene complex 4 is much less basic than conventional olefination reagents such as phosphorus ylides, it can be employed for the olefination of carbonyl compounds possessing highly acidic a-protons or of highly hindered ketones, and has become an indispensable tool in organic synthesis. Various methods for the preparation of titaniumcarbonyl olefination. This chapter focuses on the use of metal-carbene complexes and some related species in carbonyl olefination (Scheme 4.2). 

Eisch and Piotrowski reported the preparation of gem-dizinc compounds from diiodomethane and zinc powder in the titanocene chloride mediated methylenation of ketones in 1983 (equation 5)7. In this case, it was not mentioned that they had used pyrometallurgy zinc. The Tebbe-type reagent 2 was shown as an intermediary species. Before addition of titanocene chloride, the amount of methane was measured after hydrolysis of the reaction mixture to determine the formation of gem-dizinc species7. 

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