NUCLEOPHILIC ADDITIONS TO KETENES BY (TRIMETHYLSILYL)LITHIUM AND BY ENOLATES

Reaction of t-Bu2C—C—O(5) with Me3SiLi at -78 °C followed by trapping of the intermediate enolate with ac20 gave t-Bu2C=C(OAc)SiMe3 (9). Other ketenes gave similar products. Reaction of ketenes PhCR=C=O (R = Me, 13; R = Et, 3) with enolates CH2—C(OLi)R1 (R1 = H, Me, t-Bu, Ph) at -78 °C followed by warming to 25 °C and hydrolysis gave vinyl esters PhCHRC02C(R1)=CH2, along with 10% PhCHMeCOCH2COPh for R - Me, R1 = Ph. Under the same conditions the ketenes PhCR=C=0 with enolates CH2 =C(OK)R1 (R1 = Me, t-Bu, Ph) gave only 1,3-diketones PhCHRCOCH2COR1, but vinyl esters were the major products if the reactions were quenched at -78 °C. It is proposed that enolates undergo preferential O-acylation by ketenes in a kinetically favored process, but that these intermediates can revert to thermodynamically more stable C-acylated products. © 1990, American Chemical Society. All rights reserved.