CYCLIZATION OF ALKOXYIMINYL RADICALS ONTO OLEFINS - FORMATION OF 2-ALKOXY-DELTA(1)-PYRROLINES, 4,5-DIHYDROOXAZOLES AND 5,6-DIHYDROL-4H-1,3-OXAZINES

Alkoxyiminyl radicals, generated by photolysis of N-bromo imidates, un dergo exo-1,5 and exo-1,6 cyclization onto olefins on the O-alkyl side chains giving good yields of 4,5-dihydrooxazoles and 5,6-dihydro-4H-1 ,3-oxazines, respectively. exo-1,5 Cyclization onto an olefin on the i minyl side chain gives 2-alkoxy-DELTA1-pyrrolines. 4,5-Dihydrooxazole formation is more favourable than cyclization to 2-alkoxy-DELTA1-pyrro lines and both reactions are irreversible. These preferences are suppo rted by MNDO Molecular orbital calculations which predict that both pr ocesses are exothermic but cyclization onto the 0-alkenyl side chain h as a tower DELTAH(double dagger).