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

Abstract

The interaction of tris(trimethylsilyl) phosphite (TMSO) 3P and E-trifluoromethyl-β-alkoxyenones CF 3C(O)CH CHOEt and CF 3C(O)CH C(OMe)Me yielded mixtures of E-1,2- and Z-1,4-adducts, CF 3C(OTMS)[P(O)(OTMS) 2]C CH(OAlk)R 2 and CF 3(OTMS)C CHCR(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 CF 3C(OH)[P(O)(OH) 2]CH 2COMe in 88% yield, whereas hydrolysis of 2a (R = H and Alk = Et) with KOH in methanol gave CF 3C(OH)[P(O)(OK) 2]CH CHOEt in 37% yield. Acid hydrolysis of 3a (R = H and Alk = Et) and 3b (R and Alk = Me) gave phosphonic acid CF 3C(OH) 2CH CHP(O)(OH) 2 in 82% yield and trifluoromethylated 1,2λ 5σ 4-oxaphosphol-3-en.