A HORNER-WITTIG APPROACH TO S,N-KETENE ACETALS - ACID-CATALYZED HYDROLYSIS OF S,N-KETENE ACETALS TO (S)-THIOESTERS

The synthesis of S,N-acetals of formyldiphenylphosphine oxide 2 is des cribed. The stable lithiated anions of these acetals were applied in a Horner-Winig reaction with several structural types of aldehydes. The resulting S,N-ketene acetals 1 were obtained in excellent yields. Ket ones and pivaidehyde did not react with the sterically hindered phosph ine oxide anions. S,N-ketene acetals 1 were found to be selectively hy drolyzed, under mildly acidic conditions, to the Corresponding (S)-thi oesters 5. This, previously undescribed, reactivity of S,N-ketene acet als 1 allowed the two-step conversion of aldehydes into homologous (S) -thioesters 5 in good yields. Copyright (C) 1996 Elsevier Science Ltd