New novel derivatives of 1-(5/6-mono substituted or 5,6-disubstituted benzo [d] oxazol-2-yl) methyl)-6-(4- substituted phenoxy)-4,8-dihydro-1H-[1,3,2] dioxaphosphepino [5,6-d] imidazole-6-oxide (8a-f as per Scheme-1) were prepared by condensation of 4-substituted phenyl phosphorodichloridates (7a-f) with 1-(5/6-mono substituted or 5,6-disubstituted benzo [d] oxazol-2-yl)methyl) -1H-imidazole-4,5-diyl) dimethanol (6a-f). The synthons (6a-f) obtained by deprotection of isopropylidene of 1-(5/6-mono substituted or 5,6-disubstituted benzo [d] oxazol-2-yl) methyl)-6,6-dimethyl-4,8-dihydro-1H-[1,3]- dioxepino [5,6-d] imidazole (5a-f). The synthons (5a-f) were obtained by the reaction of 2-(6, 6-dimethyl-4,8-dihydro-1H-[1,3] dioxepino[5,6-d] imidazole-1-yl) acetic acid (3) with 4/5- mono substituted or 4,5-di substituted 2-amino phenols (4a-f). Similar procedure was adapted to prepare 1-( benzo [d] thiazol-2-yl ) methyl ) -6-(4-substituted phenoxy)-4,8-dihydro-1H-[1,3,2] dioxaphosphepino [5,6-d] imidazole-6- oxide (12a-f according to Scheme-2).