The photochemistry of α-azidocinnamates - A reinvestigation

Article abstract of DOI:10.1016/S0040-4020(98)00537-7

α-Azidocinnamates have been reported elsewhere to yield one diastereomer of a trimer in a stepwise and efficient manner by photolysis using quartz equipment. We find that use of pyrex filters or ketone sensitisation instead of quartz leads to high yields of the presumed intermediate diastereomeric pair of aziridinoimidazoline dimers, as does brief irradiation in quartz. These dimers have been characterised by spectral and crystallographic methods, and shown to oxidise with DDQ to give imidazoledicarboxylic esters, while the action of base on both dimer diastereomers leads to one rearranged dimer, a 1,2-dihydropyrimidine. Surprisingly, only a mixture of both diastereomeric dimers gives the trimer on further photolysis.