From Ketal

Starting with known butylated ketal-acid 85, readily synthesized in high yield directly from ketal-acid 32, deketalization as before with oxalic acid treated silica gel gave comparable results to before, with keto-acid 86 being produced in 85%... 

A soln. of p-toluenesulfonic acid in acetic anhydride added to a stirred soln. of cholestanone 3-a-0-y -S-ethylene hemithioketal in methylene chloride, after 45 min. cooled to 0°, treated with more acetic anhydride and pyridine 2-(2 -cholesten-3 -yl)-3-( -acetylthioethoxy)-2-cholestene. Y 85%. F. e., also from ketals and enol-ethers, s. G. Karmas, J. Org. Chem. 33, 2436 (1968). 

Sodium/liq. ammonia Reductive opening of heterocycles by alkali metals in liq. ammonia Hydrocarbons from ketals... 

Nucleophiles other than hydrides can be used, such as aUylsilanes, siloxy-dienes, or silyl enol ethers, to access substituted THPs from cyclic ketals. Rych-novsky et al. and Wipf et al. synthesized one THP of leucascandrolide A from ketal 76 by using a nucleophilic addition of aUylsilane in the presence of BF3 Et20. The diastereoselectivity of the reaction was explained by an axial attack on the half-chair oxocarbenium intermediate. The double bond was then transformed into the corresponding aldehyde by ozonolysis to afibrd further functionalizations (Scheme 38) (2001JA8420 2002CC2066). 

This rearrangement was appfted to the formation of the THF unit present in (-)-citreoviral starting from ketal 80. Worthy of note is the control of the four stereogenic centers in intermediate 81 achieved during the Prins-pinacol sequence (Scheme 40) (20000L223). 

Rhodium-alumina hydrogen chloride Ethers from ketals s. 17, 104... 

Camphor sulfonic acid quinoline Enolethers from ketals... 

Enolethers from ketals with alkoxyl interchange... 

Sodium alcohol 2- thylenealcohols from ketals with transesterification... 

The Claisen rearrangement of vinyl allyl ethers is a powerful reaction for the preparation of yS-unsaturated carbonyl compounds. The regioselectivity of the ketal version of this reaction has been studied, the results aiding the understanding and prediction of products formed from ketals of unsymmetrical ketones [equation (34)]. The allyl vinyl ether may also be formed by proto-... 

Tetralkyl-silanes, -germanes, and -stannanes, as well as disilanes and distannanes, have been successfully used as alkyl radical precursors. The use of alkyl radicals is closely parallel to that presented above starting from ketals for the substitutive alkylation of aromatics and the conjugate addition to alkenes and alkynes (see Equations 4.5 and 4.28). Notice, however, that the final result depends on the sensitizer-trap used. Thus, N-methylacridinium perchlorate is reductively alkylated by hexamethyldisilane but undergoes reductive dimerization with the corresponding digermanes and distannanes. "... 

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