Diastereoselective ring expansion rearrangements of (benzocyclobutenone)- and (benzocyclobutenedione)chromium complexes: Syntheses of substituted 1-indanone and 1,3-indandione complexes

Organolithium and Grignard reagents add to the oxo group of (benzocyclobute none)tricarbonylchromium(0) (1) diastereoselectively from the exo face of t he organic ligand. If acyl anion equivalents are used as nucleophiles, depr otection of the carbonyl functions of the adducts causes ring expansion rea ctions to occur. Among these a rare example of an anion-accelerated 1-vinyl cyclobutenol-cyclohexadienol rearrangement is reported which results, after isomerization, in a naphthol complex. Other ring expansion reactions gave coordinated substituted indanone derivatives, The facial differentiation by the tricarbonylchromium moiety allows for the first time the determination of the distereoselectivity of these reactions. The 1-oxoindan-2-ol derivat ives obtained can undergo an alpha-ketol rearrangement with formation of th e corresponding 2-oxoindan-1-ol complexes. Some of these reactions were per formed with nonracemic starting material in order to determine how far chir ality transfer from the planar chiral starting material to C-2 in the indan one system was possible. The ring expansion was also feasible with the benz ocyclobutenedione complex as a starting compound, the reaction giving subst ituted 1,3-indandione complexes, Crystal structure analyses of three of the complexes prepared are reported.