SYNTHESIS AND CHARACTERIZATION OF BETA-PHOSPHAENONES - AN INVESTIGATION ON THE CONJUGATIVE PROPERTIES OF THE P=C BOND

Thermally and air-stable beta-phosphaenones were synthesized by functi onalization of MesP=CCl2 (1; Mes* = supermesityl = 2,4,6-tri-tert-but ylphenyl). At low temperature, 1 was lithiated by halogen-metal exchan ge with n-butyllithium to give the phosphanylidene carbenoid (Z)-MesP =C(Cl)Li [(Z)-2] which reacted with acid chlorides to furnish the C-ca rbonyl-substituted phosphaalkenes (Z)-MesP=C(Cl)R (3: R = COtBu; 4: R = COPh; 5: R = COOEt). The reaction of (Z)-2 with carbon dioxide furn ished the carboxylate 6, which was converted by treatment with pivaloy l chloride or trimethylsilyl chloride into the phosphaalkenes 7 and 8 functionalized at the carbon atom by an anhydride or a trimethylsilyl ester function, respectively. Acidification of 6 or hydrolysis of 8 wi th water in chloroform solution afforded the novel carboxylic acid (Z) -MesP=C(Cl)COOH (9). Spectroscopic investigations (NMR, UV, IR) of 3- 9 and the X-ray structures of 3 and 4 are presented. Based on these pr operties and on theoretical calculations, the occurrence of conjugatio n in the beta-phosphaenone system is discussed and compared with the w ell-known conjugation in normal enones.