In spite of the high natural abundance of titanium, only relatively few synthetic applications of organotitanium compounds have emerged thusfar. Unlike many other elements, titanium is generally nontoxic and relatively inexpensive while it exhibits unusual chemical diversity and reactivity. In the past several years we have engaged in a program aimed at the development of new synthetic methods involving organotitanium compounds.

Our major effort in this area has focussed on a new and synthetically useful method for the olefination of various carbonyl compounds by using dialkyl titanocene derivatives. This mild titanium-mediated process is suitable for the olefination of not only aldehydes and ketones, but also various hetereoatom-substituted carbonyls, including: esters, lactones, silyl esters, anhydrides, carbonates, thioesters, selenoesters, acylsilanes, amides and imides. This process is also suitable for the olefination of enolizable ketones and acid-sensitive substrates.

In addition to dimethyl titanocene, which is useful for carbonyl methylenations, similar reactivity is possible with other dialkyl titanocenes, including dibenzyl, bistrimethylsilylmethyl and biscyclopropyl derivatives. Moreover, the use of alkenyl titanocenes leads to the conversion of carbonyls to allenes. Other synthetic and mechanistic studies of dialkyl titanocene derivatives have involved their chemistry with alkynes and their use in the polymerization of alkenes. Our initial discoveries and subsequent studies in organotitanium chemistry have already led to a number synthetic applications by us and others, including some applications in the pharmaceutical industry.