Friedel-crafts cyclisation—VI: Polyphosphoric acid-catalysed reactions of crotonophenones and chalcones |
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Authors: | J.M. Allen K.M. Johnston J.F. Jones R.G. Shotter |
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Affiliation: | The Chemical Laboratory, School of Engineering and Science, The Polytechnic of Central London, 115 New Cavendish Street, London W1M 8JS, England |
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Abstract: | Polyphosphoric acid-catalysed cyclisation of derivatives of crotonophenone and chalcone is shown to be a general reaction which occurs without migration of aryl substituents evident with other Friedel-Crafts catalysts. Two other reactions, however, may intervene: hydrogenation and α-carbonyl cleavage. Thus 4-bromochalcone gives 3 - (p - bromophenyl) -1 - phenylpropan -1 - one, 3 - (p - bromophenyl)indan -1 - one and some benzole acid. A mechanism for the cyclisation is discussed in comparison with those reported for cyclisations of α,β-unsaturated esters and divinyl ketones. The formation of intermediate Wheland complexes is predicted to be conrotatory. |
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