ORGANIC SYNTHESES VIA TRANSITION-METAL COMPLEXES .59. CYCLOBUTANIMINES FROM CARBENECHROMIUM OR CARBENETUNGSTEN COMPLEXES, ISOCYANIDES, AND ALKENES BY [2+2]-CYCLOADDITION REACTIONS OF KETENIMINE COMPLEXES - LIGAND DISENGAGEMENT WITH PYRIDINE

10-Iminotricyclo[5.3.0.0(2,9)]deca-3,5-diene complexes syn/anti-4 are obtained in yields higher than 90% by the addition of isocyanides RNC 2 [R = c-C6H11 (a), CH3 (b)] to (cycloheptatrien-1-ylmethyl)carbene complexes L(n)M = C(OEt)CH2(C7H7) 1 [L(n)M = Cr(CO)5 (a), W(CO)5 (b)]. The reactions involve an intermediate formation of ketenimine complexes L(n)M[RN = C = C(OEt)CH2C7H7] 3 by the insertion of 2 into the M = C bonds of 1. Complexes 3 isomerize to give the cyclobutanimines 4 by an intramolecular [2s + 2a]-cycloaddition reaction of the ketenimine to the alkene unit. The structure of an ti-4 c has been determined by a crystal structure analysis. Complexes 4 react with pyridine by the fragmentation of the four-membered ring to yield a tetrahydroazulen-1-imine 6 which was hydrolyzed to the corresponding ketone 7; 7 is also obtained along an independent route by the photolysis of 1a in the presence of carbon monoxide. The first isolated product of the latter reaction is the tricyclo[5.3.0.0(2,9)]deca-3,5-dienone 9, which presumably is formed via an intermediate ketene complex N and the tricyclic ketone O; 9 on warming with pyridine rearranges to 7.