P-Cl bond-induced lactamization of 2(2'-hydroxyl)phenyloxazoline to form a cyclic phosphinite, 3-(2-chloroethyl)-2-phenyl-2H-benzo[e][1,3,2]oxaza-phosphinin-4(3H)-one: synthesis, structural studies and transition metal complexes.

The equimolar reaction between 2(2'-hydroxy)phenyloxazoline (1) and PPhCl2 in the presence of triethylamine afforded an unexpected cyclic product, phenyl-benzo-oxazaphosphininone (2), instead of a simple phosphinite derivative A. A similar reaction between 1 and PPhCl2 in 2 : 1 ratio also yielded the same product 2, but with one equivalent of 2(2'-hydroxy)phenyloxazoline (1) left unreacted. The formation of the cyclic product 2 is due to the P-Cl bond induced oxazoline ring opening followed by the formation of a six-membered γ-lactam type product, 3-(2-chloroethyl)-2-phenyl-2H-benzo[e][1,3,2]oxazaphosphinin-4(3H)-one (2 also referred to as L). The reactions of 2 with H2O2, elemental sulphur or elemental selenium yielded the corresponding chalcogenides, LE (3, E = O; 4, E = S; 5, E = Se) in quantitative yield. Treatment of 2 with [Ru(η(6)-Cymene)Cl2]2, [Pd(COD)Cl2] and [Pd(η(3)-C3H5)Cl]2 resulted in the formation of [RuCl2(η(6)-cymene)(L)] (6), [PdCl2{L}2] (7), and [Pd(η(3)-C3H5)Cl(L)] (8), respectively. The compound 2 obtained in the 2 : 1 reaction when treated with [Pd(η(3)-C3H5)Cl]2 gave the same palladium complex 8 (referred to as 9a), but co-crystallized with bis(oxazolyl)palladacycle (9b) as confirmed by single crystal X-ray analysis.