Unsaturated nitriles, selective

Because the unsaturated nitrile does not react with osmium tetroxide as rapidly as a simple A holefin, selectivity between other unsaturated centers is difficult to achieve. 

Reductions. Magnesium methanol has been used for selective reduction of a,/ -unsaturated nitriles (6, 351) and amides1 and of 1,1- and 1,2-diphenyl-substituted ethylenes.2... 

Aromatic and aliphatic nitriles react with trimethylsilane by Si-H addition across the C-N triple bond. A variety of functional groups can be tolerated, although reaction rates appear to be affected by electronic and steric characteristics of the substrates. For a,/3-unsaturated nitriles, consecutive 1,2- and 1,4-addition of two equivalents of HSiMe3 occurs to selectively yield Z- or / A A-disilylenamines. 

Z)-a,f - Unsaturated nitriles. A highly selective synthesis of essentially pure (Z )-a,/ -unsaturated nitriles from aldehydes is possible by use of 1 (equation I).1... 

Giese and coworkers determined on the basis of experimental results obtained by Scheffold et al. [268, 299] that addition reactions of alkyl bromides 249 to a,p-unsaturated nitriles or esters 248 catalyzed by cobalamine 247 are free radical reactions (Fig. 61) [300], This conclusion was based on the similar cis/trans-selectivities in addition reactions of the 4-tert-butylcyclohexyl radical to different electron-poor alkenes 248 using 247 as a catalyst on one hand and classical tributyltin hydride conditions on the other. The kinetics of the radical addition was determined. 

The indium hydride compound, generated in situ from sodium borohydride and a catalytic amount of indium(m) chloride, selectively reduces carbon-carbon double bonds in conjugated alkenes such as a,a-dicyano olefins, a,/3-unsaturated nitriles, cyano esters, cyanophosphonates, diesters, and ketones (Scheme 107).372 This combined reagent system in acetonitrile reduces exclusively the a,/3-carbon-carbon double bond in a,/3,7,<5-unsaturated diaryl ketones, dicarboxylic esters, cyano esters, and dicyano compounds (Scheme 108).373... 

Effenberger, F. and Oswald, S. 2001b. (i )-Selective hydrolysis of (ii,Z)-a,P-unsaturated nitriles by the recombinant nitrilase AtNITl from Arabidopsis thaliana. Tetrahedron ... 

Unsaturated nitriles are converted smoothly to the saturated compounds by selective hydrogenation over palladinized charcoal or by chemical reduction. " The reaction is of special value in the preparation of a variety of substituted cyano compounds from the olefinic nitriles obtained in cyanoacetic ester condensations (method 387). 

Cationic Rh complexes [RhL(C0)(PPh3)2]C104 (L = unsaturated nitrile) show catalytic activities for the hydrogenation of a,3-unsaturated nitriles under mild conditions (30 °C). Selective reduction of the carbon-carbon double bonds of a,3-unsaturated carbonyls also occurs in high yield with [ Rh( 1,5-hexa-diene)Cl 2] and a phase transfer catalyst in aqueous media. ... 

Propanol doped on dehydrated alumina reduces various aldehydes and ketones at room temperature to the corresponding alcohols. a,p-Unsaturated aldehydes are selectively reduced under these conditions to the corresponding allylic alcohols. For example, citral is converted to geraniol in 88% yield. a,p-Unsaturated nitriles are reduced to saturated nitriles with triethylamine-formic acid azeotrope in... 

The reduction of intermediately formed, isolable unsaturated nitriles opens up an easy route to regio- and stereo-chemically pure unsaturated aldehydes. The overall reaction is a regio- and stereo-selective hydroformylation of alkynes [61]. 

The activation of light saturated hydrocarbons becomes increasingly more difficult as the molecules become smaller, with methane reactions being the most difficult to control. On the other hand, the occurrence of non-catalysed gas phase oxidation makes selectivity control very complicted. This is a problem common to almost all oxidations, unless one of the products is extremely stable examples are unsaturated nitriles (e.g. acrylonitrile in the ammoxidation of propane) or maleic anhydride (in the oxidation of butane). There is a parallel trend in the changes of reactivity with molecular weight in catalytic and non catalytic (gas phase) oxidation. The challenge to catalysis to achieve selective reactions at lower temperature is thus equally important for all light hydrocarbons. 

Selective reduction of the olefin unit of the a,p-unsaturated nitrile is accomplished essentially with two systems one by catalytic hydrogenation using Pd/C, the other using magnesium in MeOH, a reagent combination known for its ability to reduce a,P-unsaturated nitriles. 

Takayanagi, H., Z-Selective formation of trisubstituted a,P-unsaturated nitrile by the Horner-Emmons reaction. Tetrahedron Lett., 35, 1581, 1994. 

Noteworthy was the increase of the selectivity in water toward the 1 1 adduct when using nitromethane. Under slightly alkaline conditions, cetyltrimethylam-monium chloride was shown to catalyze the addition of various nitroalkanes onto conjugated enones [176]. Amines also reacted in aqueous Michael additions, especially with a, -unsaturated nitriles [177]. The lack of apparent reactivity of a, -unsaturated esters comes from the reverse reaction which is particularly accelerated in water. In these amine additions, water activation was compared with high pressure giving support to the implication of the hydrophobic effect. A related reaction is the Baylis-Hillman reaction which proceeds readily in water with a good rate enhancement (Scheme 34) [178]. 

A selective reduction of unsaturated nitrile presents no difficulty, Pd being the most popular catalyst ... 

Selective reduction of unsaturated nitriles presents little difficulty, and palladium is a popular catalyst for this . Even tetrasubstituted double bonds can be selectively reduced, in the presence of a nitrile function, over platinum dioxide ... 

Early extensive accounts of the 4v participation of a,/)-unsaturated carbonyl compounds in [4 + 2] cycloadditions detailed their reactions with electron-deficient dienophiles including a,/3-unsaturated nitriles, aldehydes, and ketones simple unactivated olefins including allylic alcohols and electron-rich dienophiles including enol ethers, enamines, vinyl carbamates, and vinyl ureas.23-25 31-33 Subsequent efforts have recognized the preferential participation of simple a,/3-unsaturated carbonyl compounds (a,/3-unsaturated aldehydes > ketones > esters) in inverse electron demand [4 + 2] cycloadditions and have further explored their [4 + 2]-cycloaddition reactions with enol ethers,34-48 acetylenic ethers,48 49 ke-tene acetals,36-50 enamines,4151-60-66 ynamines,61-63 ketene aminals,66 and selected simple olefins64-65 (Scheme 7-1). Additional examples may be found in Table 7-1. 

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