Chemoselective ring opening of benzoxazaphosphinines

Cyclization of 2-[(4-chloroanilino)methyl]phenol (1) with thiophosphoryl chloride afforded 2-chloro-3-(4-chlorophenyl)-3,4-dihydro-2H-1,3,2λ⁵-benzoxazaphosphinine-2-thione (2). Reaction of 2 with various heterocyclic amines (3) in the presence of Et₃N/NaH gave 3-(4-chlorophenyl)-2-nitrogen heterocyclic substituted-3,4-dihydro-2H-1,3,2λ⁵-benzoxaza-phosphinine-2-thiones (4). Further reaction of 4 with the N-sodium salt of amino heterocyclics in the presence of HCl at 50-60 °C opened the benzoxazaphosphinine ring chemoselectively at the endocyclic P-O bond and yielded 2-[4-chloro(heterocyclic substituted-phosphorothioyl)anilino]methylphenols 5-13.