Y-Ketoacetals

Ammonium ceric nitrate dissolved in 8 4 1 methanol/ethyl methyl ketone/isopropenyl acetate, after 20-25 min at room temp. aq. NaHC03 added, and the mixture heated at 40° for ca. 45 min with vigorous stirring -> product. Y 78%. The method is highly regiospecific. F.e., also synthesis of y-ketoacetals with addition of 2 C-atoms using vinyl acetate, and with dimethyl malonate in place of ketones, s. E. Baciocchi et al.. Tetrahedron Letters 28, 5357-60 (1987). 

Piperidinium acetate 3 Cyano-2-pyridones from y -ketoacetals s. 17, 830... 

The authors used (5)-carvotanacetone (dihydrocarvone) as starting material (Scheme 34). To prepare the linearly conjugated sUylenol ether, they used the Kharash protocol and attained y-alkylation by Mukaiyama aldol reaction with trimethylorthoformate (195). The ketoacetal 295 was a-hydroxylated according to Rubottom by silylenol ether formation followed by epoxidation and silyl migration. Acid treatment transformed 296 to the epimeric cyclic acetals 297 and 298. endo-Aceta 297 was equilibrated thereby increasing the amount of exo-acetal 298. The necessary unsaturated side chain for the prospected radical cyclization was introduced by 1,4-addition of a (trimethylsilyl)butynylcopper compound. 

Oxidocycloheptanones. A soln. of l,3-bis(trimethylsiloxy)-l-methoxy-l,3-buta-diene (as 1,3-dicarbanion equivalent) in methylene chloride treated sequentially with 1 eq. TiCl4 and startg. ketoaldehyde in the same solvent at - 78° product. Y 66%. F.e. incl. 3,7-oxidocyclooctanones, also with diketones and ketoacetals as biselec-trophile, s. G.A. Molander, S.W. Andrews, Tetrahedron Letters 30, 2351-4 (1989). 

With functionalized allylic bromides, the same procedure allowed preparation of bromo-homoallylic alcohols and 1,3-ketoacetates (Mandai et al., 1984) or a-methylene-y-butyrolactones (Nokami et al., 1986). 

Aroxyacoxy compds. a-Diketone monoketals Enolperoxides Glycidic acid esters a-Hydroxyacetals 1-Hydroxylactones a-Ketoacetals a-Keto-Y-lactones Lactolesters... 

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