Organische Synthesen mit Übergangsmetall‐Komplexen, 59[1] Cyclobutanimine aus Carbenchrom‐ oder ‐wolfram‐Komplexen, Isocyaniden und Alkenen durch [2 + 2]‐Cycloadditionen intermediärer Ketenimin‐Komplexe; Liganden‐Abspaltung mit Pyridin

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Abstract
Organic Syntheses via Transition Metal Complexes, 59[1]. – Cyclobutanimines from Carbenechromium or ‐tungsten Complexes, Isocyanides, and Alkenes by [2 + 2]‐Cycloaddition Reactions of Ketenimine Complexes; Ligand Disengagement with Pyridine10‐Iminotricyclo[5.3.0.02,9]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 LnM=C(OEt)CH2(C7H7) 1 [LnM = Cr(CO)5 (a), W(CO)5 (b)]. The reactions involve an intermediate formation of ketenimine complexes LnM[RN=C=C(OEt)CH2C7H7] 3 by the insertion of 2 into the M=C bonds of 1. Complexes 3 isomerize to give the cyclo‐butanimines 4 by an intramolecular [2s + 2a]‐cycloaddition reaction of the ketenimine to the alkene unit. The structure of anti‐4c 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[5.3.0.02,9]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.

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