Tricarbonylchromium complexes with methoxy substituted benzocyclobutenone and benzocyclobutenedione ligands

The syntheses of methoxy substituted benzocyclobutenone and benzocyclobuten edione tricarbonylchromium complexes rac-4 and rac-10 are reported. rac-4 i s preferentially obtained by a [2 + 2] cycloaddition of 3-methoxy-1,2-dehyd robenzene with diethoxyethene followed by complexation and acetal hydrolysi s, whereas rac-10 is prepared by acetalization of the ligand followed by co mplexation and hydrolysis. rac-4 is st stereoselectively reduced to the ben zocyclobutenol complex with LiAlH4 in high yield. However, the anion driven ring opening-cycloaddition sequence furnished only poor selectivity. Vinyl Grignard addition to the 3-methoxybenzocyclobutenedione complex rac-10 gav e the 1-vinyl adduct, which was characterized by an X-ray structure analysi s. (C) 1999 Elsevier Science S.A. All rights reserved.