Nucleophilic Additions to Ketenes by (Trimethylsilyl)lithium and by Enolates

Article abstract of DOI:10.1021/jo00298a047

Reaction of t-Bu2C=C=O (5) with Me3SiLi at -78 deg C followed by trapping of the intermediate enolate with Ac2O 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 deg C followed by warming to 25 deg C and hydrolysis gave vinyl esters PhCHRCO2C(R¹)=CH2, along with 10 percent PhCHMeCOCH2COPh for R = Me, R¹ = Ph.Under the same conditions the ketenes PhCR=C=O 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 deg 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.