ON THE REGIOCHEMISTRY OF CYCLOADDITION OF UNSYMMETRICAL ARYNE WITH NITRONE REMARKABLE EFFECT OF TRIALKYSILYL SUBSTITUENT

Regioselectivity of the aryne-nitrone cycloaddition was studied. Vario us unsymmetrical arynes with C(3)-substituent were generated at -78-de grees-C by halogen-lithium exchange of ortho-haloaryl triflate and tra pped with a nitrone. The sense and magnitude of the regio-controlling effect posed by the substituent is discussed based on the electronic a nd steric grounds by assuming the non-synchronous, charge-controlled t ransition state. The trialkylsilyl group, by its strong electron-relea sing property, poses a remarkable effect on the regioselectivity.