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Synthesis 1986; 1986(2): 122-125
DOI: 10.1055/s-1986-31492
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Halogenative Deoxygenation of Ketones; Vinyl Bromides and/or gem-Dibromides by Cleavage of 1,3-Benzodioxoles (Ketone Phenylene Acetals) with Boron Tribromide

Elio Napolitano* , Rita Fiaschi, Ettore Mastrorilli
  • *Istituto di Chimica Organica, Facoltà di Farmacia, Via Bonanno 6, I-56100 Pisa, Italy
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Publikationsdatum:
20. August 2002 (online)

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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-Benzodioxole 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 significance. 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.