| abstract |
PURPOSE: To readily provide an essential amino acid derivative, the subject compound, in a high yield without passing via a thiol ester, by reacting a novel compound with a carbonyl compound in the presence of a boron triflate, etc., and a base. n CONSTITUTION: A compound of formula I [R 1 is a protecting group of formula -XH (X is O, S, etc.); R 2 is H, lower alkyl, cycloalkyl, etc.; R 3 is carboxy- protecting group] is reacted with a compound of formula II (R 4 is the same as R 2 ; R 5 is H or the same as R 2 ) in the presence of boron triflate or tin triflate and a base (e.g., Na 2 CO 3 , NaOH, etc.) to provide an α-substituted β- hydroxycarboxylic acid ester of formula III. The method permits to avoid the low yield preparation of the objective compound carrsed by the self-condensation reaction thereof and to enlarge the range of the compounds to be applied because of enabling to perform the reaction under neutral conditions. Also when the compound of formula I (R 2 is H) is used, by-products are not produced. n COPYRIGHT: (C)1989,JPO&Japio |