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

The interaction of tris(trimethylsilyl) phosphite (TMSO)(3)P and E-trifluoromethyl-beta-alkoxyenones CF3C(O)CH=CHOEt and CF3C(O)CH=C(OMe)Me yielded mixtures of E-1,2- and Z-1,4-adducts, CF3C(OTMS)[P(O)(OTMS)(2)]C=CH(OAlk)R 2 and CF3(OTMS)C=CH-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 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)]CH=CHOEt in 37% yield. Acid hydrolysis of 3a (R. = H and Alk = Et) and 3b (R and Alk = Me) gave phosphonic acid CF3C(OH)(2)CH=CHP(O)(OH)(2) in 82% yield and trifluoromethylated 1,2 lambda(5)sigma(4)-oxaphosphol-3-en. (c) 2005 Elsevier B.V. All rights reserved.