Silyl ketene acetals from butyrolactone

When R is replaced by a smaller group, and R is large (TMS, Bu ), then both Ai and S3 gauche interaction between R and R ) are disfavored compared to Si, and the syn isomers are obtained (Table 1 entries 14-17). The same analysis applies to several other cases ketene bis(trimethylsilyl) acetals (R = OTMS) are anti selective when R is Me (anti 86-89%) and syn selective when R is Bu (syn 70-89%) silyl ketene acetal (3) derived from butyrolactone is anti selective when R = H (anti... 

When R3 is replaced by a smaller group, and R2 is large (TMS, Bu1), then both Ai and S.i (gauche interaction between R and R2) are disfavored compared to Si, and the syn isomers are obtained (Table 1 entries 14-17). The same analysis applies to several other cases ketene bis(trimethylsilyl) acetals (R3 = OTMS) are anti selective when R2 is Me (anti 86-89%) and syn selective when R2 is Bu1 (syn 70-89%) 24 silyl ketene acetal (3) derived from butyrolactone is anti (R Ji ) selective when R = H (anti 70%) and syn (R, S ) selective when R = TMS (single isomer, equation 2) 25a c S-trimethylsilyl S,N-acetals (4) are anti selective when R = Me (anti 60-87%) and syn selective when R = Pr (syn 60%, equation 3).22 Cyclic enol silanes usually show poor selectivity,2 1026 apart from isolated cases where good anti. syn ratios were obtained by carefully choosing reagents and Lewis acids. Fair anti preferences were observed with the cyclopentenone-derived silyl enol ether and TiCU (equation 4 R = Pr1, Bn anti (R Ji ) syn(R, S ) >90 10)27 and with 2-trimethylsilyloxyfuran (5 equation 5 anti (R, R ) syn(R, S ) 76—88 24—12).17-27... 

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