Stereochemistry of the photoisomerisation of 4-methylenebicyclo[3,1,0]hex-2-enes to spiro[2,4]hepta-4,6-dienes
Abstract
The photochemical isomerisation of a 4-methylenebicyclo[3,1,0]hex-2-ene derivative to a spiro[2,4]hepta-4,6-diene proceeds with a high degree of stereospecificity and is interpreted in terms of an excited state sigmatropic 1,5-shift followed by a thermal 1,5-shift.