Reaction of trifluoromethylated β-alkoxyenones with tris(trimethylsilyl) phosphite: A temperature influence on regioselectivity

The interaction of tris(trimethylsilyl) phosphite (TMSO)3P and E-trifluoromethyl-β-alkoxyenones CF3C(O)CHCHOEt and CF3C(O)CHC(OMe)Me yielded mixtures of E-1,2- and Z-1,4-adducts, CF3C(OTMS)[P(O)(OTMS)2]CCH(OAlk)R 2 and CF3(OTMS)CCHCR(OAlk)[P(O)(OTMS)2] 3 where R and Alk = H and Me, or both Me. Conversion of these 1,2-adducts to 1,4-isomers was effected by increased temperature or by exposure to more tris(trimethylsilyl) phosphite. Acid hydrolysis of 2b (R and Alk = Me) gave ketophosphonic acid CF3C(OH)[P(O)(OH)2]CH2COMe in 88% yield, whereas hydrolysis of 2a (R = H and Alk = Et) with KOH in methanol gave CF3C(OH)[P(O)(OK)2]CHCHOEt in 37% yield. Acid hydrolysis of 3a (R = H and Alk = Et) and 3b (R and Alk = Me) gave phosphonic acid CF3C(OH)2CHCHP(O)(OH)2 in 82% yield and trifluoromethylated 1,2λ5σ4-oxaphosphol-3-en.