Transition-metal carbonyl complexes derived from cyclo-octa-2,4,6- trienone and cyclohepta-2,4,6-trienone

Abstract

Acid-catalysed hydrolysis of methoxycyclo-octatetraene, (3), is a convenient route to cycle-octa-2,4,6-trienone, (1). The reaction of (3) with dodecacarbonyl-triangulo-tri-iron affords tricarbonyl(η-methoxycyclo-octatetraene)iron, which on acid-catalysed hydrolysis gives tricarbonyl(2–5-η-cyclo-octa-2,4.6-trienone)iron, (6); use of deuteriated acid yields (6) stereospecifically monodeuteriated in the anti-8-position. Treatment of (1) with (benzylideneacetone)tricarbonyliron gives the tricarbonyliron complex of bicyclo[4.2.0]octa-2,4-dien-7-one, the bicyclic valence isomer of (1). The reaction of tricarbonyl(η-cyclohepta-2,4,6.trienone)iron with diazomethane does not lead to ring expansion, but gives a pyraroline by regiospecific 1,3-dipolar cycloaddition. Thermolysis of the pyrazoline, and its analogue prepared using [²H₂]diazomethane, yields the corresponding tricarbonyliron complexes of bicyclo[5.1.0]octa-3,5-dienone.