HOMOLYTIC SUBSTITUTION BY IMINYL RADICAL AT SELENIUM - A FREE-RADICAL ROUTE TO 1,2-BENZOSELENAZOLES

Thiohydroxamic esters (3) derived from the O-carboxymethyl oxime derivatives (2) of 2-(benzylseleno)benzaldehyde (1:R = H), 2-(benzylseleno)acetophenone (1:R = Me) and 2-(benzylseleno)propiophenone (1:R = Et) decompose smoothly, upon irradiation, with the loss of carbon dioxide and formaldehyde to give the 1,2-benzoseknazoles (5). The reaction presumably involves the iminyl radical intermediate (4) which undergoes intramolecular free-radical homolytic substitution at selenium to afford the product (5).