Studies in the Cycloproparene Series: Approaches to Cyclopropaheteroarenes

Abstract

Photolysis of the pyrazolopyridazines (3) results in the loss of nitrogen. The resultant diradicals (5) do not close to the cyclopropa [d]pyridazines (4) but undergo 1,4-hydrogen transfer to afford the 8-(2'-propenyl)pyridazines (6) instead. In the presence of trapping agents diradicals (5)give ethers (7) with methanol, epoxycyclohepta [d]pyridazines (8) with furan, and the 1,4- and 1,2-addition products (16) and (17) respectively, with butadiene. The formation of (8) and (16)provides the first examples of 1,4-addition of a 1,3-diradical to a diene.