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The reactive 16e-species Cp2Ti=CH2 can be generated in situ from either its aluminum alkyl adducts or olefin adducts (metallacyclobutanes). This complex reacts with a wide variety of unsaturated functionalities including :;;c=O, :::c=C~, -c=c-and -C=N. In most instances the ;:c:O groups are methylenated. Key to the utility of these complexes is their lack of basic properties in contrast with phosphorous ylides; all of the normal "Wittig" side reactions are eliminated using these reagents. Acid chlorides and anhydrides are converted into enolate complexes, which can be used in aldol type chemistry. The combination of the reactivity toward C=O and C=C results in an efficient method for the conversion of unhindered carbonyl centers into quarternary carbon centers. BACKGROUNDAlkylidene complexes of high oxidation state transition metals have been recognized for the past several years. They were first proposed as intermediates in numerous reactions (1), and have been isolated recently as tantalum (2), tungsten (3), and titanium (4) complexes. The low valent analogs prepared earlier show different types of reactions and trends in stability (5). The high oxidation state complexes /CH 3

The titanium alkylidene 1 (Tebbe's reagent) is a versatile methylenation agent for the conversion of ketones to olefins and esters to vinyl ethers (eq l).1 Unfortunately, this commercially available reagent (Strem, Alfa) is exf Contribution No. 7126.

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