Heterocyclic rearrangements. Part V. Transformations of 3,5-diacetyl-4-chloromethyl-1,4-dihydro-2,6-dimethylpyridine

Abstract

The title compound (Ia) undergoes the expected ring expansion to 3,6-diacetyl-4,5-dihydro-2,7-dimethyl-1H-azepine-4-carbonitrile (II) when treated with cyanide ion. When treated with water, (Ia) gives 3,5-diacetyl-4-(2-acetyl-3-oxobutyl)-1,4-dihydro-2,6-dimethylpyridine (IIIa) and a rearrangement product, 4-acetyl-2-(1-acetyl-2-oxopropyl)-2,3-dihydro-5-methylfuran (V). Pyrolysis of the dihydrofuran (V) yields 3,6-bis-(1-hydroxyethylidene)oct-4-ene-2,7-dione (VI) whereas hydrolysis gives the fulvene, 1,3-diacetyl-5-(1-hydroxyethylidene)-2-methylcyclopenta-1,3-diene (VII), 3-acetylpentane-1,4-dione (IX) and acetylacetone. Proof of structure is presented and a synthesis of compound (IX) is described. The tautomerism of compound (IX) and the mechanism of the rearrangements of compounds (Ia) and (IIIa) are discussed.