Mechanism of heterocyclic ring expansions. Part V. Base-catalysed rearrangement of 2-dichloromethyl-2,5-dimethyl-2H-pyrrole and related compounds

Journal of the Chemical Society C: Organic Pub Date: DOI: 10.1039/J39690002255

Abstract

2-Dichloromethyl-2,5-dimethyl-2H-pyrrole gave 2-ethoxymethyl-5-methylpyridine with sodium ethoxide, 2,5-dimethylpyridine with sodium hydride, and, in a more extensive rearrangement, trans-1,2-di-5-methyl-2-pyridylethylene with potassium hydroxide.

With sodium ethoxide 2-dichloromethyl-2,3,4,5-tetramethyl-2H-pyrrole gave 2-ethoxymethyl-3,4,5-trimethylpyridine and 4-ethoxymethyl-2,3,5-trimethylpyridine, 2-dichloromethyl-3,4-dimethyl-2,5-diphenyl-2H-pyrrole gave 4-ethoxymethyl-3-methyl-2,5-diphenylpyridine, and 4-dichloromethyl-3,4,5-trimethyl-4H-pyrazole gave 3-ethoxymethyl-4,6-dimethylpyridazine. Yields were generally in the order of 80%.

A unifying mechanism viabicyclic[3,1,0] intermediates is proposed for this apparently general rearrangement of dichloromethyl-2H-pyrroles with active hydrogen atoms.

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