Stephen reduction

There are two principal methods for the reduction of nitriles to aldehydes. In one of these, known as the Stephen reduction, the nitrile is treated with HCl to form... 

This is redueed with anhydrous SnCl2 to RCH=NH, which precipitates as a complex with SnC and is then hydrolyzed (16-2) to the aldehyde. The Stephen reduction is most successful when R is aromatic, but it can be done for aliphatic R up to about six carbons. It is also possible to prepare 21 in a different way, by treating ArCONHPh with PCI5, which can then be converted to the aldehyde. This is known as the Sonn-Muller method. 

The complex hydride reductions of nitriles to aldehydes compare favorably with the classical Stephen reduction which consists of treatment of a nitrile with anhydrous stannous chloride and gaseous hydrogen chloride in ether or diethylene glycol and applies to both aliphatic and aromatic nitriles [183,285, 1152]. An advantage of the Stephen method is its applicability to polyfunctional compounds containing reducible groups such as carbonyl that is reduced by hydrides but not by stannous chloride [1153]. 

A procedure for the preparation of o-tolualdehyde from o-toluanilide by the Sonn-Miiller method has been published in Organic Syntheses. In addition to the alternative methods of preparation listed there, o-tolualdehyde has been prepared from o-xylyl bromide and hexamethylenetetramine, by the Stephen reduction of o-tolunitrile, and by the procedure of the present preparation. ... 

The Stephen reduction has been applied to a variety of nitriles, but is genuinely useful only for aromatic substrates. Table 11 gives a number of representative examples, and more are available elsewhere. The failure with o-toluonitrile is untypical, and was attributed to steric hindrance. A variant employing tin(II) bromide was successful in synthesizing cinnamaldehyde and its vinylog (45) in 65% and 50% yields, respectively. ... 

Table 11 Yields of Aldehydes Prepared by the Stephen Reduction of Aromatic Nitriles ...

One of the classical reductive aldehyde syntheses is the Sonn-MUller reduction of imidoyl chlorides. The method is closely related to the Stephen reduction described in the previous section. As shown in Scheme 16, substrates (53) may be prepared either by the treatment of anilides with phosphorus pentachloride or sulfinyl chloride, or less usually via the Beckmann rearrangement. They are... 

Formylbenzenesulfonamide has been prepared by chromic acid oxidation of -toluenesulfonamide, the Sommelet reaction on p-chloromethylbenzenesulfonamide, and by the Stephen reduction of j -cyanobenzenesulfonamide. The present method provides a general procedure for the synthesis of substituted aromatic aldehydes as illustrated in Table I. 

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