REGIOCONTROLLED FUNCTIONALIZATION OF 7-MEMBERED RING VIA NUCLEOPHILICCYCLOHEPTENYL-ETA(3)-ALLYLTITANIUM COMPLEXES

A new ''electron-reversed'' method for the functionalization of a seve n-membered ring is developed. Cycloheptenyl-eta(3)-allyltitanocene com plexes derived from cycloheptatriene react with aldehydes or carbon di oxide to afford, respectively, the mixture of isomeric 1,4- and 1,3-cy cloheptadienyl carbinols 3a-e and 2a-e or methyl esters 7 and 6. The 3 /2 and 7/6 ratios increase with increasing steric hindrance in the ele ctrophile. Moreover, these may be significantly increased by introduci ng tert-butyl substituents on the Cp rings of the starting titanocene dichloride. The regiochemistry of the reaction was rationalized in ter ms of the equilibrium between the two envisageable allylic complexes. The reaction constitutes the first direct entry to functionalized 1,4- cycloheptadienes, some of which are related to biologically active com pounds.