2,5-Bisdiazomethylfuran: A Novel Entry to the C6H4O Surface

Warming the dilithium salt 7 of furan-2,5-dicarboxaldehyde bis(tosylhydrazone) to 110°C and subsequently trapping the products in solid argon at 10 K resulted in the formation of 1-diazo-hex-3-en-5-yn-2-one (9). The intermediate 2,5-bis(diazomethylfuran) (6) is too labile to be directly observed under these conditions. The formation of 9 from 6 is rationalized by the loss of one nitrogen molecule and rapid rearrangement of the intermediate carbene 8. Photolysis of 9 leads to loss of the second nitrogen molecule and rearrangement of the resulting carbene 12. The major path is the Wolff rearrangement to hexa-1,3-dien-5-yn-1-one (11); the minor path is the intramolecular cycloaddition of the carbene center to the triple bond to 1H-bicyclo[3.1.0]hexa-3,5-dien-2-one (2). UV photolysis of 2 results in the ring opening to yield again ketene 11. The mechanism of this rearrangement was investigated by deuterium labeling.