Metal-assisted cycloadditions. Part 3. Reactions of dicarbonyl(η5-cyclopentadienyl)(η1-2-methoxyallyl)iron with electron-deficient olefins and acetylenes

Abstract

Dicarbonyl(η⁵-cyclopentadienyl)(η¹-2-methoxyailyl)iron (3) has been treated with a number of tetra-, tri-, and disubstituted electron-deficient olefins and acetylenes. A mixture of cyclic and linear products has been formed from reaction of complex (3) with trimethyl ethylenetricarboxylate and diethyl 1 -cyanoethylene-1,2-dicarboxylate, with exclusive formation of the cyclopentyl-Fp adduct from ethyl 3,3- and 2,3-dicyanoacrylates. Reaction of complex (3) with tetramethyl ethylenetetracarboxylate, its tetraethyl analogue, diethyl methylenemalonate, t-butylcyanoketen, and dimethyl acetylenedicarboxylate has given, on the other hand, only linear adducts arising from H-transfer. Demetallation of the (η¹-3,3-dicyano-4-ethoxycarbonyl-1-methoxycyclopentyl)-Fp complex (6b) with ceric ammonium nitrate and carbon monoxide has given a mixture of the corresponding cyclopentanone dimethyl acetal and olefin derivatives.