Formiminium salts reduction

Finally, it may be useful to note a method which, although not actually a reduction, has the same overall effect of transforming RCO2H to RCHO. As shown in Scheme 3, the acid (6) is doubly deproto-nated then treated with a formiminium salt (7). Carbon-carbon bond formation is followed by loss of CO2 and methoxide to give enamine (8), which can be isolated or transformed by acid hydrolysis to the corresponding aldehyde. The scope and efficiency of the method are difficult to judge accurately, as the... 

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