Special features of reaction of 2-(5-methyl-2-phenyl-2H-1,2,3- diazaphosphol-4-yl)-4H-benzo[D]-1,3,2-dioxaphosphorin-4-one with diethyl mesoxalate

Mixed anhydrides of salicylic and phosphoric (phosphonic) acids, salicylphosphites (phosphonites), are convenient and available reagents for the synthesis of derivatives of tetraand pentacoordinate phosphorus owing to the presence of the energy-rich Р–О bond [1]. Introducing to the atom of the tricoordinate phosphorus an additional diazaphosphol fragment containing a bicoordinate phosphorus could have both affected the regiochemistry of reactions of the salicylphosphites with activated carbonyl compounds and led to the formation of new reaction products. In this study by the reaction of previously described [2] 4-(dichlorophosphino)-5-methyl-2-phenyl-2H1,2,3-diaza phosphol with bis(О-trimethylsilyl) derivative of salicylic acid we prepared for the fi rst time 2-(5-methyl-2-phenyl-2H-1,2,3-diazaphosphol-4-yl)4H-benzo[d]-1,3,2-dioxaphosphorin-4-one (I) containing two phosphorus atoms of different coordination at a carbon atom (P=C–P) and investigated its reaction with diethyl mesoxalate. Common phosphorus derivatives of hydroxycarboxylic acids react with this compound forming phosphoranes and leaving intact the anhydride Р–О bond [3]; the introduction to the atom of the tricoordinate phosphorus of an isocyanate group leads to the formation of products of bicyclononane structure [4]. Although the molecule of compound I contains a reactive bicoordinate P atom, the reaction occurs exclusively at the tricoordinate P atom resulting in the formation of 2-(5-methyl-2-phenyl-2H-1,2,3-diazaphosphol-4-yl)2,5-dioxo-4,4-bis(diethyldicarbonyl)benzo[2,3-f]-1,3,2dioxaphosphepine (II). Thus 5-methyl-2-phenyl-2H1,2,3-diazaphosphol-4-yl substituent apparently owing to its electronic and steric effects directed the reaction to the path uncharacteristic of the diethyl mesoxalate involving