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14.1.1.1.1 Method 1: [C1 + C3 + C1] Diacylation of Propene and Higher Alkenes

DOI: 10.1055/sos-SD-014-00002

Balaban, T. S.; Balaban, A. T.Science of Synthesis, (20031425.

The acylation of alkenes catalyzed by Lewis or Brønsted acids has been studied for more than a century.[‌95‌] For example, it is known that 2-methylpropene (isobutylene) affords 4-methylpent-3-en-2-one on monoacetylation. The discovery that its diacetylation furnished 2,4,6-trimethylpyrylium salts was made independently in 1959 by Balaban and Nenitzescu in Romania,[‌19‌] and Praill in England.[‌18‌] Later it was shown that the aluminum trichloride catalyzed reaction between acetyl chloride and tert-butyl chloride, followed by decomposition of the reaction mixture with water, allowed the isolation of the triacetylation product of 2-methylpropene (a vinylogous 4-pyrone),[‌96‌] and, finally, Roussel found that decomposition of the same mixture with liquid ammonia resulted in a tetraacetylation product, isolated as the 2,7-diazanaphthalene (no dioxonia analogue could be isolated).[‌97‌‌99‌] Actually, it was shown that the tetraacylation product is formed first and is then deacylated to the triacylation product. It is interesting to mention that the discovery of this reaction in Bucharest[‌19‌] occurred serendipitously during a one-pot assembly of five synthons: 2,6-di-tert-butyl-4-methylpyrylium salts were isolated in low yields from the reaction of aluminum trichloride with tert-butyl chloride and carbon monoxide under pressure. 2-Methylpropene was diacylated by the pivaloyl cation intermediate, formed from carbon monoxide and the tert-butyl cation.[‌19‌]

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