Nitriles from boranes

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

Methylpropionitrile added all at once to a soln. of di(isopinocampheyl)borane prepared from borane and (+)-2-pinene in tetrahydrofuran, stirred 0.5 hr., coned, in vacuo to remove excess nitrile, redissolved in tetrahydrofuran, acetone cyanohydrin added, after 15 min. the crude intermediate a-aminonitrile isolated, and heated 10 hrs. at 75° in aq. WCl (R)(-)-valine. Y 45%. F. e. s. U.E. Diner et al., Tetrah. Let. 1972, 3145. 

Monocarbaborane cluster chemistry is sparsely investigated compared to its flanking fields of binary boron hydride cluster chemistry and dicarbaborane cluster chemistry. Dicarbaborane compounds can be synthesized relatively easily by addition of alkynes to boron hydrides such as decaborane, but there are no simple routes to monocarbaborane compounds. Traditionally, the principal methods involve removal of one carbon atom from dicarbaboranes, or addition of cyanide or organic nitriles to borane clusters to give C-aminated monocarbaboranes, which can subsequently be deaminated. ... 

Trialkylboranes react rapidly and in high yields with a-halo ketones,a-halo esters, a-halo nitriles, and a-halo sulfonyl derivatives (sulfones, sulfonic esters, sulfonamides) in the presence of a base to give, respectively, alkylated ketones, esters, nitriles, and sulfonyl derivatives. Potassium tert-butoxide is often a suitable base, but potassium 2,6-di-tert-butylphenoxide at 0°C in THF gives better results in most cases, possibly because the large bulk of the two tert-buXy groups prevents the base from coordinating with the R3B. The trialkylboranes are prepared by treatment of 3 mol of an alkene with 1 mol of BH3 (15-16). With appropriate boranes, the R group transferred to a-halo ketones, nitriles, and esters can be vinylic, or (for a-halo ketones and esters) aryl. " °... 

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... 

Simlilar conclusions are indicated for the reaction product obtained from dichloro-acetonitrile and trichloroborane. For the product obtained from chloroacetonitrile and trichloroborane, however, a nitrile-borane structure is found which, according to the authors 481, might depend critically on the reaction conditions. 

The alkylation of activated halogen compounds is one of several reactions of trialkyl-boranes developed by H. C. Brown1560 (see also 5-12, 5-19, 8-24 to 8-28, etc ). These compounds are extremely versatile and can be used for the preparation of many types of compounds. In this reaction, for example, an alkene (through the BR3 prepared from it) can be coupled to a ketone, a nitrile, a carboxylic ester, or a sulfonyl derivative. Note that this is still another indirect way to alkylate a ketone (see 0-95) or a carboxylic acid (see 0-96), and provides an additional alternative to the malonic ester and acetoacetic ester syntheses (0-94). 

The following reactions proceed with the participation of the allylic boron system (i) allylboration and protolytic cleavage of organic compounds with multiple bonds, (ii) allylboron-alkyne condensation,598 599 (iii) reductive mono-and trans-a,a -diallylation of nitrogen aromatic compounds, (iv) disproportionation processes between tribut-2-enylborane and BX3 (X = C1, Br, OR, SR). Allylboration of carbonyl compounds, thioketones, imines, or nitriles leads to the homoallylic alcohols, thiols, or amines (Equations (136) and (137). It is most important that 1,2-addition to aldehydes and imines proceeds with high diastereoselectivity so that ( )-allylic boranes and boronates give the anti-products, while -products are formed preferentially from (Z)-isomers. 

Another novel approach to labelling molecules with carbon-11 has been published by Somawardhana, Sajjad and Lambrecht . These workers have absorbed one of the reactants required for the synthesis on a solid support and the reaction has been done by adding the other reagents to the solid support and heating the mixture in a sealed vial. One example illustrating their methodology is the formation of [l- C]putrescine. The H CN is trapped on a potassium-hydroxide-coated silica gel. Then, acrylonitrile is added, and the reaction tube sealed at both ends. After the tube had been heated at 75 °C for 5 minutes, the Michael addition product was eluted from the solid support and the solvent evaporated. Finally, the nitrile groups were reduced with a borane-dimethylsulphide complex in THF (equation 77). The total reaction time was less than 40 minutes and the product was obtained in a 53% radiochemical yield. 

This chapter describes newly discovered reactions and synthetic utilities of lithium aminoborohydrides (LABs) including (1) the reduction of nitriles to amines, (2) the direct synthesis of amine-borane complexes from LABs and benzylic or alkyl halides (nitrogen transfer), and (3) the tandem nitrogen transfer/reduction of halogen-substituted benzonit-riles to give the corresponding aminobenzylamines. 

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