Ketones added hydrogen

The selective hydrogenation of the double bond of an a,p-unsaturated carbonyl compound is rather easily accomplished over most metal catalysts under moderate conditions. Because double bond isomerization does not take place in these systems, palladium catalysts are often used in the liquid phase at ambient temperature and atmospheric pressure. An added advantage here is that palladium is essentially inert for aliphatic aldehyde and ketone hydrogenations under these conditions. Vapor phase hydrogenations should be run at temperatures as low as possible to minimize carbonyl group hydrogenations. Catalysts such as Ni(B) are... 

The ketone is added to LiNt -Pr)2 (LDA), a strong base, which removes an a hydrogen from the ketone to produce an enoiate. 

The carbon-oxygen double bond of the carbonyl group is opened, and the hydrogen sulfite radical is added. An increase in temperature reverses the reaction more easily for ketones than for aldehydes. 

The use of acetone cyanohydrin (in an exchange reaction) instead of alcoholic hydrogen cyanide affords even higher yields of 17-cyanohydrins and the former reagent has the added advantage of reacting quantitatively and essentially selectively with the 17-ketone of androst-4-ene-3,17-dione. Sodium hydroxide promotes the exchange reaction in some cases. 

In ketones existing largely as the enol, palladium may prove effective in minimizing hydrogenolysis, Hydrogen was added slereoselectively to the least hindered side of L-ascorbic add (3) to give L-gulono-1,4-lactone (4)... 

Aryl radicals are produced in the decomposition of alkylazobenzenes and diazonium salts, and by f)-scission of aroyloxy radicals (Scheme 3.73). Aryl radicals have been reported to react by aromatic subsitution (e.g. of Sh) or abstract hydrogen (e.g. from MMA10) in competition with adding to a monomer double bond. However, these processes typically account for <1% of the total. The degree of specificity for tail vs head addition is also very high. Significant head addition has been observed only where tail addition is retarded by sleric factors e.g. methyl crotonate10 and -substituted methyl vinyl ketones 79, 84). 

When secondary amines are added to aldehydes or ketones, the initially formed N,N-disubstituted hemiaminals (14) cannot lose water in the same way, and it is possible to isolate them. However, they are generally unstable, and under the reaction conditions usually react further. If no a hydrogen is present, 10 is converted... 

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