Organo-zirconium reagents

Preparation of benzisothiazoles, butenolides or pyrroles using organo-zirconium reagents and acetylenes. 

Zirconium-aluminum analogs of the Tebbe reagent have been reported to react with carbonyl compounds slowly, in low yield or not at all. However, zirconium aUcylidenes which are stabilized by a phosphorus rather than an aluminum ligand do transfer their alkylidene moiety to carbonyl. These results provide some of the few examples of long chain alkylidene transfer to ca nyl from an organo-metallic reagent (equation 31). 

The chemoselectivity of organo-titanium and -zirconium reagents is practically unaffected by the nature of the nucleophilic moiety of their molecule. Although aldehydes always react much faster than ketones, the addition rates sometimes differ significantly, depending upon steric and electronic properties... 

The chemoselectivity between aldehydes and ketones has been studied by Kauffinann et al Cerium reagents exhibit moderate aldehyde selectivities, although these are much lower than those of the organo-metallic reagents of titanium, zirconium and chrmnium (Scheme 2). ... 

Whilst Grignard and organolithium reagents are most widely employed, they are by no means exclusive. Organo-zirconium, silicon, tin, copper, zinc, cadmium, and mercury compounds have... 

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