Reductions of Aliphatic and Aromatic Nitriles to Primary Amines with Diisopropylaminoborane

Abstract

Diisopropylaminoborane [BH(2)N(iPr)(2)] in the presence of a catalytic amount of lithium borohydride (LiBH(4)) reduces a large variety of aliphatic and aromatic nitriles in excellent yields. BH(2)N(iPr)(2) can be prepared by two methods: first by reacting diisopropylamineborane [(iPr)(2)N:BH(3)] with 1.1 equiv of n-butyllithium (n-BuLi) followed by methyl iodide (MeI), or reacting iPrN:BH(3) with 1 equiv of n-BuLi followed by trimethylsilyl chloride (TMSCl). BH(2)N(iPr)(2) prepared with MeI was found to reduce benzonitriles to the corresponding benzylamines at ambient temperatures, whereas diisopropylaminoborane prepared with TMSCl does not reduce nitriles unless a catalytic amount of a lithium ion source, such as LiBH(4) or lithium tetraphenylborate (LiBPh(4)), is added to the reaction. The reductions of benzonitriles with one or more electron-withdrawing groups on the aromatic ring generally occur much faster with higher yields. For example, 2,4-dichlorobenzonitrile was successfully reduced to 2,4-dichlorobenzylamine in 99% yield after 5 h at 25 degrees C. On the other hand, benzonitriles containing electron-donating groups on the aromatic ring require refluxing in tetrahydrofuran (THF) for complete reduction. For instance, 4-methoxybenzonitrile was successfully reduced to 4-methoxybenzylamine in 80% yield. Aliphatic nitriles can also be reduced by the BH(2)N(iPr)(2)/cat. LiBH(4) reducing system. Benzyl cyanide was reduced to phenethylamine in 83% yield. BH(2)N(iPr)(2) can also reduce nitriles in the presence of unconjugated alkenes and alkynes such as the reduction of 2-hexynenitrile to hex-5-yn-1-amine in 80% yield. Unfortunately, selective reduction of a nitrile in the presence of an aldehyde is not possible as aldehydes are reduced along with the nitrile. However, selective reduction of the nitrile group at 25 degrees C in the presence of an ester is possible as long as the nitrile group is activated by an electron-withdrawing substituent. It should be pointed out that lithium aminoborohydrides (LABs) do not reduce nitriles under ambient conditions and behave as bases with aliphatic nitriles as well as nitriles containing acidic alpha-protons. Consequently, both LABs and BH(2)N(iPr)(2) are complementary to each other and offer methods for the selective reductions of multifunctional compounds.

Iron‐Catalysed Borylation of Arenediazonium Salts to Give Access to Arylboron Derivatives via Aryl(amino)boranes at Room Temperature

“…In that case, we thought about using this unusual reactivity in combination with the known reactivity of ferrocene with arenediazonium salts leading to arylferricinium intermediates before further rearrangement 16. If some reactions have been described using areneadiazonium salts for borylation with bis(pinacolato)diboron17 1b even very recently,18 one might expect a completely different reactivity in the presence of such a reducing agent as an aminoborane 19. Side reactions may include reduction of the diazonium salt into the arene or the aniline, and (or) reduction of the catalyst.…”

Ruthenium‐Catalyzed Tandem Activation of C≡N and B−H Bonds under Dihydrogen: Synthesis of BN Heterocycles

“…Compound 4 a formally resulted from reduction of the nitrile function and activation of the B−H bond, which led, for the first time, to the formation of the cyclic 1 H ‐2,1‐benzazaborole featuring a NH group. The reaction was catalyzed under a dihydrogen atmosphere, and notably, no 1,1‐bis(boryl)amine oligomers formally resulting from double B−H insertion– were detected. The scope of the reaction was extended to 2‐cyanophenyl(amino)boranes displaying different arene substitution patterns.…”

Simple Preparation of New Potential Bioactive Nitrogen-Containing Molecules and Their Spectroscopy Analysis

“…In this case, the integrity of most of the benzylamines is compromised when they are exposed to air moisture or even stored at low temperatures for a long period of time (Nazih & Heissler, 2002). A way to prevent this effects is based on choosing an appropriate strategy that enables the preparation of the desired amount benzylamines at lower cost than those acquired commercially, which could be possible by reduction of nitriles (Haddenham et al, 2009) and oximes (Gannett et al, 1988).…”