MECHANISM OF HETEROCYCLIC RING EXPANSIONS .V. BASE-CATALYSED REARRANGEMENT OF 2-DICHLOROMETHYL-2,5-DIMETHYL-2H-PYRROLE AND RELATED COMPOUNDS

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