Photochemistry of 2-azido-2-alkyl-3-oxobutanoic esters and amides

Photolysis of 2-alkyl-2-azido-3-oxobutanoic esters and amides gave products resulting from alkyl or acyl migration onto nitrogen. The resulting ketimimes could be isolated in moderate purity, but the N-acyl imines were rapidly converted into solvation products or enamides (N-acetyl dehydroamino acid esters) resulting from double bond migration. Mechanisms for formation of these products are discussed. The N-(2-azido-2-methyl-3-oxobutanoyl) derivative of the diketopiperazine from L -valyl- L -proline gave a stereoisomer of the cyclol tripeptide unit of ergovaline. Keywords: N-acyl imines, mechanism of 2-azido-3-keto ester photolysis, cyclol tripeptide synthesis, ergovaline.