Nitriles, reaction with borane

Reaction of halo nitriles or diazo nitriles with boranes... 

Primary amino methylene substituents were introduced by a sequence of cya-nodehalogenation and subsequent reduction of the resulting nitrile with borane dimethyl sulfide. To incorporate tertiary aminomethylene substituents into the 2-pyri-done framework, a microwave-assisted Mannich reaction using preformed iminium salts proved to be effective. 

The reaction can be extended to ot,ot-dihalo esters1557 and a,a-dihalo nitriles.1558 It is possible to replace just one halogen or both. In the latter case the two alkyl groups can be the same or different. When dialkylation is applied to dihalo nitriles, the two alkyl groups can be primary or secondary, but with dihalo esters, dialkylation is limited to primary R. Another extension is the reaction of boranes with -y-halo-a.p-unsaturated esters.1559 Alkylation takes place in the -y position, but the double bond migrates, e.g.,... 

The reaction of 154 with chloroacetonitrile in the presence of potassium /-butoxide afforded 155. The nitrile group was reduced with borane methyl sulfide to the corresponding amine 156, which on treatment with sodium methoxide was transformed into the 1,4-oxazepine 157 (Scheme 23) <1996JOC6060>. 

The reaction of alkenes with borane, monoalkyl and dialkylboranes leads to a new organoborane (see 15-16). Treatment of organoboranes with alkaline H2O2 oxidizes trialkylboranes to esters of boric acid." This reaction does not affect double or triple bonds, aldehydes, ketones, halides, or nitriles that may be present elsewhere in the molecule. There is no rearrangement of the R group itself, and this reaction is a step in the hydroboration method of converting alkenes to alcohols (15-16). The mechanism has been formulated as involving initial formation of an ate complex when the hydroperoxide anion attacks the electrophilic boron... 

Reduction. This borohydride reduces nitriles to afford stable aldimine-borane complexes, which can be used to prepare homoallylic amines on further reaction with R2BCH2CH=CH2. 

Trimethylamine-tcrt-butylborane has also been used successfully in reactions with terminal alkynes (161) and nitriles (162), affording tert-butyldi(l-alkenyl)boranes and dimeric alkylideneamine-Icrt-butylboranes (XV), respectively. 

The chemistry of iminoborane compounds containing the X>N—B< moiety has developed only within the last decade. The first representatives of this type of compounds were obtained by hydroboration of nitriles with sterically hindered boranes 10> or tetraalkyldiboranes 17> the resultant compounds appeared to be unique intermediates (stabilized by steric or reactivity effects) in the course of reactions that normally lead to borazines. The intermediates illustrated in Eq. (1) are mostly unstable at room temperature and, in general, cannot be isolated. 

This cited reaction illustrates that the C=N double bond of iminoboranes is quite stable. Indeed, the C=N bond in these compounds tends to increase its bond order, forming corresponding nitriles, rather than to undergo further 1,2-additions leading to aminoboranes. This suggestion is confirmed by several reported transformations of iminoboranes to nitrile-borane adducts (Eq. (20)) M). Addition across the C=N double bond of iminoboranes is virtually unknown. This event is also true for related imines (e.g., dichloromethylenealkyl-amines) which yield imine-trihaloborane adducts with trihaloboranes rather than to undergo a 1,2-addition (c.f. Sect. VII). 

The reaction of tris(organothio)boranes with nitriles leads to B—S substituted iminoboranes. 1,2-addition of tris(methylthio)borane or tris(phenylthio) borane to trichloroacetonitrile yields the monomeric products (XIV) or (XV)32). 

Reactions of tris(organothio)boranes with a-halogenated nitriles are very slow (c.f. (II)). Analogous reactions of tris(organothio)boranes with acetonitrile could not be accomplished. 

Monomeric and dimeric species obtained from the reaction of alkylthio-cyanates with tris(phenylthio)borane have not been isolated in a pure state 32). The reaction of (organothio)dichloroboranes with nitriles as illustrated by... 

Imine-borane bonds which are incorporated into annular systems appear to be considerably more stable. A number of such compounds has been prepared by the reaction of nitriles with (cyclohexenylamino)boranes 7>. 

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