Aldehydes, metal catalysed amidation

The catalysed oxidative amidation of aldehydes to form amides has been reported with copper sulfate in the presence of a base and TBHP oxidant. This catalyst exhibited activity in synthesising primary secondary, tertiary and amides from aldehydes. Although the oxidant is required in stoichiometric quantities, these transformations generally require low metal catalyst loadings of only 5 mol%, low temperatures of 80 °C and short reaction times (Scheme 17.23). 

Several more expensive metals have been reported to form primary amides from aldehydes via an oxime intermediate. One of these is the iridium catalyst [Ir(Cp )Cl2]2, which is able, in a one pot reaction, to convert alcohols into amides (Scheme 17.37). This involves firstly the oxidation of the alcohol to the aldehyde. This is then converted to the oxime on addition of hydro-jylamine, which can then undergo a metal catalysed rearrangement to the corresponding amide. ... 

Ligand free metal (Rh,Ru,Ir)-catalysed oxidation of alcohols to corresponding aldehydes, either by atmospheric O2 or oxidants, has proved to be more effective in Af-alkylation reaction cycles for the synthesis of amide/amine derivatives, compared to the usual anaerobic dehydrogenative process. The method was general in substrate scope and tolerated various amides, amines, and alcohols. ... 

New Cj-symmetric nickel complexes of a-amino amides catalyse enantioselective addition of dialkylzincs to aldehydes DFT studies suggest that the aldehyde carbonyl, rather than coordinating to the metal, is activated by an amino hydrogen which has been acidified by the nickel complexation. 

Alkali metal t-butoxides, hydrides and bis(TMS)amides efficiently catalyse Claisen-Tishchenko disproportionation of aldehydes to the corresponding carboxylic esters. Potassium bases were more effective than sodium, and 18-crown-6 further accelerates the reaction. Kinetic studies suggest that the rate-determining step is a second-order concerted hydride transfer from a potassium hemiacetal to another molecule of aldehyde. 

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