Imine salts from nitriles

The tetrachloroferrate or tetralluoroborate salts of alkylated alkyl- or aryl-nitriles (nitrilium ions) are reduced to imines with triethylsilane. Subsequent hydrolysis of the intermediate imines leads to aldehydes in good yields, thus providing an excellent overall route to aldehydes from nitriles (Eq. 338).28,562... 

Discussed in this chapter, for the most part, are documented cases where complexes derived from (one or more equivalents of) a Grignard or organolithium reagent, in combination with a copperfl) salt, have been used to add to an aldehyde, ketone, imine, amide or nitrile moiety. In the majority of examples, the key issue is one of stereocontrol. Hence, where available, data within the organocopper manifold versus those for other organometallic reagents are provided for comparison. 

The early stages of the reaction of the quaternary salt can be regarded as proceeding in a manner exactly analogous to that by which the isoxazoles themselves are degraded, the j8-oxoketene imine structure (148) being one mesomeric form of a compound which could alternatively be formulated as a nitrilium betaine. However, by contrast with the products from the isoxazoles (i.e., enolates of /3-keto-nitriles), this is electrically neutral and susceptible to further nucleophilic attack. 

In principle, it would appear that the presence of bulky substituents R and E should kinetically favor the formation of nitrile imines. Lithium salts have been used for much of this work and it has been shown that this is generally the case [e.g., for 151 (X = S)] bulky electrophiles favor the nitrile imine (e.g., 153) while smaller analogues favor diazo compounds (e.g., 152). Reducing the size of the substituent on the diazo compound has a similar effect (e.g., 150 from 151) (X = lone pair). 

Nitriles having at least one hydrogen on the functional carbon, react with trimethylchlorosilane under electrochemical conditions to provide a mixture of silazanes and enamines of acylsilanes. These enamines have been suggested to be formed from the isomeric ketene imine form of the nitrile. They were obtained as a mixture of Z (major) and E isomers. Treatment of the silazane-enamine mixture with trimethylchloro-silane/methanol and sodium borohydride followed by neutralization of the salt gives the corresponding RSMA.191... 

Indoles have been prepared from reactions of o-aminophenylketones with reactive , or stable " arsonium ylides. Oxo-stabilized ylides reacted with 2-chloro-oximes to give trans-5-acyl-A -isoxazolines, and isoxazoles have been obtained from reactive arsonium ylides and a-isonitrosoketones, and from triphenylarsonium methylide and nitrile oxides The latter ylide reacts similarly with nitrile imines to give pyrazoles. With triphenylarsonium benzylides and benzoylylides,benzene diazonium salts give 1,3,4,6-substituted 1,4-dihydro-1,2,4,5-tetrazines in a reaction in which initial coupling of the reagents is followed by a dimerisation. ... 

A few miscellaneous oxidations using oxoammonium salts generated from TEMPO or substituted TEMPO analogs have been reported in the literature. These include the electrochemical oxidation of thiols to disulfides by a TEMPO-modified felt electrode [66], the electrochemical oxidation of amines to imines or nitriles [67], the cleavage of benzyl ethers by a single electron transfer mechanism with an oxoammonium bromide salt [68], and the dibromination of propargyl acetates by catalytic oxoammonium tribromide generated from a nitroxide and bromine [69]. 

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