Ketenes enolizable, reaction with

Wolff rearrangements were also observed when most of the same acylsi-lyldiazoalkanes were photolyzed in acetone instead of benzene.21 The ketenes 185 resulting from a 1,3-methyl migration of the silene were detected in addition to the expected ene product 186 derived from the reaction of the silene with acetone (or other enolizable ketones) (Eq. 58). When R = Ad, only the cyclic siloxatene 187 was formed under the same... 

Dealkoxycarbonylation. 3-Keto esters and malonic esters with an enolizable proton ct to the ester group undergo dealkoxycarbonylation in 80-95% yield when heated in propionic acid for 24-72 hours. P-Kcto esters can also be cleaved by refluxing in acetic acid. The requirement for an a-proton suggests that the reaction involves loss of ROH to give a ketene intermediate. The propionic acid is converted into the anhydride. 

Aldol Additions to Ketones. Traditionally, cerium enolates or the Reformatsky-type reaction have been employed to achieve high-yielding aldol additions to enolizable ketones. In this regard, methyl trichlorosilyl ketene acetal provides a reliable alternative for the synthesis of tertiary -hydroxy esters. In the absence of a Lewis base promoter, the aldol additions of 1 to ketones are too slow to be synthetically useful. On the contrary, with pyridine A-oxide as catalyst, methyl trichlorosilyl ketene acetal reacts smoothly with nearly all classes of ketones (7) (Scheme 1). Good yields of the tertiary alcohol products (8) are obtained (eq 4), table 2 from aromatic (entries 1-2 and 4—6), hetereoaromatic (entry 3), olefinic (entries 7-8), acetylenic (entries 9-10), and aliphatic (entries 11-14) ketones. The only poorly performing substrate is 2-tetralone (7o), which affords a 45% yield of the addition product and returns 45% of unreacted starting material, most likely from competitive enolization. 

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