Rearrangements of 2‐ and 3‐Furfurylidene

The photo‐ and thermochemistry of diazo(2‐furyl)methane ( 3 ) and diazo(3‐furyl)methane ( 6 ) was investigated using the matrix isolation technique. Photolysis of 3 results in the formation of ( Z )‐pent‐2‐en‐4‐yn‐1‐al ( 2 ) in a clean reaction, in agreement with the observation of Shechter et al. Photolysis or pyrolysis of diazo compound 6 yields ( s‐Z )‐(α‐formyl)methylenecyclopropene ( s‐Z ‐ 13 ) as the only detectable product. Carbene 14 and cyclopropene 15 are proposed as intermediates, but not stable under the reaction conditions and thus not directly observed. The reaction sequence 6→13 provides a novel and simple route to methylenecyclopropenes.