Halogenative Deoxygenation of Ketones; Vinyl Bromides and/or<i>gem</i>-Dibromides by Cleavage of 1,3-Benzodioxoles (Ketone Phenylene Acetals) with Boron Tribromide
作者:Elio Napolitano、Rita Fiaschi、Ettore Mastrorilli
DOI:10.1055/s-1986-31492
日期:——
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.
代表性的酮1类化合物通常在良好的产率下通过酮的二甲基缩酮与1,2-二羟基苯的反式缩醛化反应,并与三溴化硼裂解,转化为相应的1,3-苯并二噁烷5。由α-非支链脂肪酮衍生的1,3-苯并二噁烷通常生成乙烯基溴和偕二溴化合物的混合物;在大多数情况下,通过选择合适的反应时间可以有选择性地获得纯的偕二溴化合物。由α-支链酮衍生的1,3-苯并二噁烷产生复杂的混合物,其裂解似乎在合成上意义不大。芳香酮的1,3-苯并二噁烷仅生成乙烯基溴。脂肪族环状偕二溴化合物3通过相转移催化脱溴反应转化为相应的乙烯基溴2。