Nitriles 2-pentenenitrile

The titanium(IV) chloride catalyzed addition of allylic silanes to (E)-(2-nitroethenyl)benzene affords y,<5-unsaturated nitronates which, on treatment with low valent titanium species [generated in situ from titanium(IV) and zinc], give y,<5-unsaturated nitriles. For example, [(Zs)-2-butenyl]-(dimethyl)phenylsilane underwent reaction with ( )-(2-nitroethenyl)benzene to give 3-methyl-2-phenyl-4-pentenenitrile in 65 % yield as a 3 1 mixture of diastereomers of unassigned configuration22. 

In asymmetric hydrocyanation reactions the desired isomers are the chiral branched products only. Good regioselectivity toward the branched product (>98%) is limited to vinylarenes. Hydrocyanation of 1,3-dienes gives a variety of mixtures depending on the catalyst and conditions 1-alkenes give the linear nitrile as major product [34]. Both are seen in the adiponitrile process in which the unwanted branched 2M3BN (hydrocyanation product from 1,3-butadiene) is isomerized to the linear product 3-pentenenitrile, which is then hydrocyanated by in-situ isomerization to 4-pentenenitrile, resulting in the linear adiponitrile. Thus vinylarenes and cyclic alkenes (mainly norbomene) are usually the substrates of choice for the asymmetric hydrocyanation. Hopefully 1,3-dienes will become feasible substrates in the near future. 

A convenient synthesis of unsaturated nitriles by a stereospecific alkylative cleavage of pyridine ring via borate process has been reported. Namely, the reaction of 2-bromo-6-lithiopyridine with trialkylboranes affords 5-alkyl-5-dialkylboryl-2-(25--4-(E)-pentadienenitriles (28), which are versatile intermediates for the preparation of 5-alkyl-2-(Z)-4-(E)-pentadienenitriles (29), 5,5-dialkyl-4-pentenenitriles (SO), and 5,5-dialkyl-2,4-pentadienenitriles (SJ), as depicted in Eq. 65 . 

The 2-pentenenitrile, 2-methyl-3-butenenitrile, and methylglutaronitrile in Figure 1.1 are by-products of this reaction sequence. duPont is still studying the phosphines used as ligands for the nickel in an effort to find one bulky enough to favor terminal addition only.214 Reduction of the various nitriles leads to the amines in Figure 1.1, including the cyclic ones. The 2,3-dichloro-l,3-buta-diene is probably a by-product in the synthesis of 2-chloro-1,3-butadiene used to make Neoprene rubber. duPont also polymerizes acrylonitrile to prepare poly (acrylonitrile) fiber (Orion). Acetonitrile is obtained as a by-product of the ammoxidation of propylene to produce acrylonitrile (reaction 1.20). 

A detailed study of hydrogenation of several alkenes and polybutadiene was undertaken using the catalysts [RhCl(HEXNa)2]2 and [RhCl(OCTNa)2]2 (HEXNa and OCTNa, Structures 8 and 9) [52] with or without an added solvent (toluene). With both catalysts the terminal alkenes were hydrogenated much faster than the internal ones, and this was also reflected in the preferential hydrogenation of the pendant vinyl units (products of 1,2-addition) in polybutadiene versus the internal double bonds (from 1,4-polymerization) (Eq. 31). Internal double bonds in 2-pen-tene- and 3-pentenenitriles were hydrogenated unusually fast compared with simple alkenes such as 1-octene, with no concomitant reduction of the nitrile group. 

The same team has also described the selective hydrogenation of cis-2-pentenenitrile with surfactant-stabiUzed ammonium perfluorotetradecanoate bimetallic Pd-Ru nanopartides prepared via in situ reduction of their simple salts in reverse micelles in SCCO2 [22]. The optimized ratio Pd Ru nanopartide (1 1) shows the highest activity for the hydrogenation of functionalised alkene under mild conditions. No hydrogenation of the terminal nitrile of the molecule in amine was observed and, finally, this fluorinated micelle-hosted bimetallic catalyst gives relevant activity and selectivity in the supercritical fluid without deactivation for at least three catalytic cycles. 

The isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile is thought to occur by elimination and re-addition of HCN. A number of labeling experiments have been conducted to reveal the order and reversibility of the steps of hydrocyanation an experiment that addresses the mechanism of isomerization of the branched nitrile is depicted in Equation 16.8. As shown on the left of this equation, allylic transposition of the nitrile group without elimination would lead to 5-deuterio-3-pentenenitrile as the only isotopomer of 3-PN-iij. However, elimination to form an H-Ni-CN complex and free 1-deuteriobutadi-ene would lead to a mixture of two labeled 3-PN-iij isotopomers after re-insertion of the labeled butadiene and reductive elimination of the free labeled 3-PN. A mixture of the two isotopomers was formed, and this result indicates that isomerization occurs by elimination and re-addition of HCN. 

Pentenenitrile is first rapidly isomerized by the nickel catalyst to 4-pentenenit-rile. Addition of hydrogen cyanide then affords adiponitrile as the major product. This is fortunate, as the unwanted conjugated 2-pentenenitrile is thermodynamically more stable than either the 3- or the 4-isomer. The favourable initial course of the isomerization is thought to be controlled by the formation of a cyclic intermediate or transition state in which the nitrile group coordinates to nickel. 

In the pastfewyears, application of electron-rich phosphine [23-27] and carbene [28] ligands has attracted some attention for the Ni-catalyzed 2M3BN isomerization reaction. These catalyst systems commonly yield 2-pentenenitriles (2PN) and branched 2-methyl-2-butenenitriles (2M2BN). Although the formation of (X,P-unsaturated nitriles 2PN and 2M2BN is of no technical relevance, it has been studied in quite some detail because the transformation is an interesting model reaction to study Ni-catalyzed C-H bond activation (Scheme 8.6). 

In all cases, no formation of a,p-unsaturated nitriles (2PN/2M2BN) was observed. This excellent selectivity for 3-pentenenitriles is particularly remarkable, considering that formation of 2PN and 2M2BN is quite common among aryl diphosphine ligands such as dppf (l,l -bis(diphenylphosphino)ferrocene, 12% other nitriles ) [24] or Xantphos (up to 50% 2PN) [41]. 

Aryl and alkyl nitriles (7), in the presence of levulinic acid, hydrogen and a catalyst can be converted to N-alkyl pyrrolidones (Figure 2). Preferred catalysts for this reduction include Ir/Si02, Ru/AbOa and Pd/C. Excellent results are obtained with low cost nitriles such as 2-and 3-pentenenitrile which are intermediates or byproducts in the production of nylon intermediates (Invista) and should be available at very low cost. Aryl nitriles such as benzonitrile can also be used to prepare N-benzyl and N-cyclohexylmethyl pyrrolidones. 

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