A Simple Route to Acylsilane En01 Esters from En01 Esters skpbeil w. Wright During the course of some recent work on silyl kttene acetals, we sought to prepare the trimetbylsilyl ketene acetal of vinyl 2-etbylbexanoate. To our surprise, the attempted conversion of this compound to the trimethylsilyl ketene acetal under standard conditions (addition of the ester in THF to 1.1 eq of LDA in THF at -78 "C, followed by quenching with 1.2 eq of Me3SiCl) afforded the product of vinyl memlation (1) instead.1 This result was surprising in light of the substantial difference in pKs that would be expected between the proton next to the carboxyl group and the vinyl proton. Furthermore, the unusual StNctum of 1. an en01 ester of an acylsilane, mpresents a structural class that heretofore has been relativtly inaccessible.2 This unexpected result prompted us to extend this metbcdology to other substrates and to examine the potential scope of this transformation. Results are summan 'xui in Table 1. It was found that addition of IDA to a premixed solution of the vinyl ester and Me$IiCl at -78 "C afforded the highest yitlds (&try la vs. lb). It will be noted that the reaction works very well with I+&SiCi and Et#iCl (Entries la, 2,s. 6,7). less so with PhzMeSiCl (Entry 3). and not at all with t-BuMe$iCl (Entry 4). Reducing the steric demand about tht proton a to the carboxyl groups (Rl = Et * Me =+ H) results in increasing formation of tbe expected silyl ketene acetal. However, in these cases the desired vinyl silyl products may be obtained in modest yield by the use of 2.2 eq IDA and 2.4 eq Me3SiCl (Entry 9).3 Attempts to intercept the putative vinyl anion respo&blt for the formation of 1 with other electrophiles, such as benzaldebyde and iodomethaue, wue unsuccessful. In these cases the starting vinyl ester was not mcoveted following standard workup. Allowing the vinyl anion to equilibrate for varying lengths of time up to 0.5 h at -78 OC prior quenching with Me@iCl did not result in a significant decrease in the yield of 1 beyond that obtained in Entry lb.