Furopyridines. IV. Unexpected dimerization of 5‐methyl‐4,5,6,7‐tetrahydrofuro[3,2‐c]‐ and 6‐methyl‐4,5,6,7‐tetrahydrofuro[2,3‐c]pyridine by acidic hydrolysis

Reaction of 5‐methyl‐4,5,6,7‐tetrahydrofuro[3,2‐c]‐ (1) and 6‐methyl‐4,5,6,7‐tetrahydrofuro[2,3‐c]pyridine (2) with hydrochloric acid gave novel dimerized compounds 3a‐d and 4a‐d, respectively. The structures of 3a, 3b, 4a and 4b were determined by spectroscopic method, and 3c, 3d, 4c and 4d by single crystal X‐ray analysis. The reaction courses for the formation of these compounds are proposed.