Halogenative Deoxygenation of Ketones; Vinyl Bromides and/or gem-Dibromides by Cleavage of 1,3-Benzodioxoles (Ketone Phenylene Acetals) with Boron Tribromide

Article abstract of DOI:10.1055/s-1986-31492

Representative ketones 1 have been converted in generally good yields to the respective 1,3-benzodioxoles 5 by trans-acetalization of ketone dimethyl acetals with 1,2-dihydroxybenzene, and cleaved with boron tribromide. 1,3-Benzodioxoles derived from α-unbranched aliphatic ketones gave in general a mixture of vinyl bromides and gem-dibromides; pure gem-dibromides could be selectively obtained in most of cases using a suitable reaction time. 1,3-Benzodioxoles derived from α-branched ketones gave complex mixtures and their cleavage appears to be of little synthetic signifance. 1,3-Benzodioxoles of aromatic ketones gave vinyl bromides only.Aliphatic cyclic gem-dibromides 3 were converted to the respective vinyl bromides 2 by phase-transfer-catalysed dehydrobromination.