ABSTRACT: Treatment of representative orthoesters (2) with pyruvonitrile (3) afforded the corresponding o, a-diethoxynitriles(4) in 65-80% yields. Depending upon the conditions used to protonate the initial adduct, subsequent addition of an organolithium(5) or Grignard reagent to the latter (4) led to the obtention of either a-imino acetals (6) or the corresponding monoprotected a-diketones (_Z) in> 90% yield.