Acrylonitrile, addition 1,2-cycloaddition with

Subsequent studies on the thermolysis of 1,2,3-selenadiazole 16 (n = Z) in the presence of a variety of alkenes (methyl acrylate, acrylonitrile, methyl vinyl ketone, methyl methacrylate, methyl 2-butenoic acid, butyl vinyl ether, and 1-octene) also afforded cycloadducts 17, in 12-76% yield with the same regiochemistry as observed for cycloadditions with 14 <2000JOM488>. Analogous cycloadditions with methyl derivatives of 16 (n = Z) as well as 16 ( = 1, 3, and 4) and ethyl acrylate was also observed in yields of 35-76% (Table 1). In addition to the cycloadduct. 

With acrylonitrile, only [2-1-2] cycloadducts 6, 8 and 9 were obtained. Additionally, bromomethylenecyclopropane underwent a [2-1-2] cycloaddition with dichloroketene yielding 3-bromo-2,2-dichlorospiro[2.3]hexan-2-one. ... 

Furan also undergoes cycloadditions with allenes," " with benzyne" and with simpler dienophiles, like acrylonitrile and acrylate various Lewis acidic catalysts can assist" in some cases, zinc iodide is one such, hafnium tetrachloride another, and improved endo exo ratios are obtained in an ionic liquid as reaction solvent. Maleate and fumarate esters react if the addition is conducted under high pressure. This device can also be used to increase markedly the reactivity of 2-methoxyfuran and 2-acetoxyfuran towards dienophiles. At higher reaction temperatures alkynes and even electron-rich alkenes will add to furan. 3- or 5-Halo-furans react faster in these cycloadditions. ... 

Jug and co-workers investigated the mechanism of cycloaddition reactions of indolizines to give substituted cycl[3,2,2]azines <1998JPO201>. Intermediates in this reaction are not isolated, giving evidence for a concerted [8+2] cycloaddition, which was consistent with results of previous theoretical calculations <1984CHEC(4)443>. Calculations were performed for a number of substituted ethenes <1998JPO201>. For methyl acrylate, acrylonitrile, and ethene, the concerted [8+2] mechanism seems favored. However, from both ab initio and semi-empirical calculations of transition states they concluded that reaction with nitroethene proceeded via a two-step intermolecular electrophilic addition/cyclization route, and dimethylaminoethene via an unprecedented two-step nucleophilic addition/cyclization mechanism (Equation 1). 

A good example for which experimental data are available, involves activation energies for Diels-Alder cycloadditions of different cyanoethylenes as dienophiles with cyclopentadiene, relative to the addition of acrylonitrile with cyclopentadiene as a standard. 

When acrylonitrile or ethyl acrylate was used as the dipolarophile, the azomethine adducts (134) and (135) were formed no thiocarbonyl ylide addition products were isolable in refluxing toluene or xylene, although the isoindoles (136a) and (136b) derived from them were isolated. In contrast to the reactions with fumaronitrile or AT-phenylmaleimide, the azomethine adducts (134) and (135) were still present at higher reaction temperatures — almost 50% in toluene and 4-5% in xylene. Under the same reaction conditions other electron-deficient dipolarophiles like dimethyl fumarate, norbornene, dimethyl maleate, phenyl isocyanate, phenyl isothiocyanate, benzoyl isothiocyanate, p-tosyl isocyanate and diphenylcyclopropenone failed to undergo cycloaddition to thienopyrrole (13), presumably due to steric interactions (77HC(30)317). 

Styrene and substituted styrenes react with tetramesityldisilene 1, tetra-tert-butyl-disilene 21, and tetrakis(tert-butyldimethylsilyl)disilene 22 to afford the corresponding disilacyclobutane derivatives.127,134 Similarly, [2 + 2] additions occur between the disilenes with a C = C double bond in an aromatic ring135 and acrylonitrile.136 Bains et al. have found that the reaction of disilene 1 with trans-styrene- provides a 7 3 diastereomeric mixture of [2 + 2] adducts, 201 and 202 [Eq. (95)] the ratio is changed, when czs-styrene-Ji is used.137 The formation of the two diastereomeric cyclic adducts is taken as the evidence for a stepwise mechanism via a diradical or dipolar intermediate for the addition, similar to the [2 + 2] cycloaddition of phenylacetylene to disilene ( )-3, which gives a 1 1 mixture of stereoiso-meric products.116,137... 

The ortho cycloaddition is thermally forbidden in a suprafacial-suprafacial manner and the photochemical reaction is forbidden with S benzene and ground-state alkene. On the basis of these considerations, it could be understood that the ortho addition had only been observed with systems where the alkene is the lowest excited singlet species (as with maleimides [37,74,75] or where either the alkene or the arene has marked acceptor properties (the only examples known at that time were benzene-acrylonitrile [127] and benzonitrile + a mono-olefin [1,73], Benzene-acrylonitrile and benzonitrile-olefin systems do not display charge-transfer absorption, but charge transfer could well follow excitation. Bryce-Smith further stated that irradiation of benzene in the presence of simple mono-olefins normally provides B2u (Si) benzene as the lowest excited singlet species, which leads to meta rather than ortho addition, but the latter process might, in principle, be able to occur under conditions where a Biu (S2) state of benzene is populated. 

Reaction of acrylonitrile with ketene acetals.3 Depending on the zinc salt and the solvent, ketene silyl acetals undergo [2+2]cycloaddition or a Michael-type addition with acrylonitrile. The former reaction occurs in CCU with ZnBr2, the latter in CH2C12 with Znl2, with no interconversion. 2-Chloroacrylonitrile can also be used in this way, but substituted acrylonitriles are inactive. 

Cycloaddition of trimethylsilyldiazomethane with activated olefins leads to pyrazoline derivatives that have the SMA substructure. Two examples are reported in the literature. The first concerns addition to acrylonitrile that gives 5-trimethylsilyl-3-cyano-A2-pyrazoline in good yield.111... 

Sensitized addition of cyclic dienes with chlorinated alkenes, employing an excess of the latter, yields mixtures of [4+2] and [2+2] adducts (Sch. 10). A substantial proportion of [4+2] adduct 46a is formed when cyclopentadiene 32 is the diene, but cyclohexadiene 36 yields almost entirely the [2+2] adduct 46b. Use of acyclic 1,3-dienes leads only to [2+2] products. The regioselectivity of the cycloadditions is consistent with a biradical intermediate 48 [47]. Sensitized irradiation of cyclopentadiene with 1-acetoxy acrylonitrile 49 also gives a [4+2] and [2+2] mixture, but with a higher proportion of the [4+2] adduct than the reactions using chloro-alkenes 45 [33-35]. 

Addition of anionic nucleophiles to alkenes and to heteronuclear double bond systems (C=0, C=S) also lies within the scope of this Section. Chloride and cyanide ions are effieient initiators of the polymerization and copolymerization of acrylonitrile in dipolar non-HBD solvents, as reported by Parker [6], Even some 1,3-dipolar cycloaddition reactions leading to heterocyclic compounds are often better carried out in dipolar non-HBD solvents in order to increase rates and yields [311], The rate of alkaline hydrolysis of ethyl and 4-nitrophenyl acetate in dimethyl sulfoxide/water mixtures increases with increasing dimethyl sulfoxide concentration due to the increased activity of the hydroxide ion. This is presumably caused by its reduced solvation in the dipolar non-HBD solvent [312, 313]. Dimethyl sulfoxide greatly accelerates the formation of oximes from carbonyl compounds and hydroxylamine, as shown for substituted 9-oxofluorenes [314]. Nucleophilic attack on carbon disulfide by cyanide ion is possible only in A,A-dimethylformamide [315]. The fluoride ion, dissolved as tetraalkylammo-nium fluoride in dipolar difluoromethane, even reacts with carbon dioxide to yield the fluorocarbonate ion, F-C02 [840]. 

Bicyclo[2.1.0]pentane (7 equation 3) readily undergoes a cycloaddition across carbon-carbon double bonds in the presence of nickel(O) complexes. The mode is formally analyzed as a thermally forbidden [2 + 2] process and is in striking contrast to that of the lower homolog, bicyclo[1.1.0]butane, which suffers cleavage of two o -bonds and affords formal allylcarbene addition products. When a solution of bi-cyclo[2.1.0]pentane (7) and [Ni(AN)2] in excess methyl acrylate is heated at 40 C for 36 h under a nitrogen atmosphere, the stereoisomeric cycloadducts exo- and c/ product methyl 3-(cyclopent-2-enyl)propionate (10a 22%). Reaction of (7) with acrylonitrile affords the corresponding adducts (8b), (9b) and (10b). 

It has been concluded that encounter complexes (or exciplexes) and ion-pairs are the key intermediates in these reactions." Addition of acrylonitrile to JV-unsubstituted imidazoles generally gives a-cyanethylation while cycloaddition products arise with JV-substituted compounds." " ... 

Stereochemical studies add great support to the proposition that [2 -i- 2] cycloadditions involve tetra-methylene diradical intermediates, for these additions take place with partial or complete loss of cisitrans stereochemical relationships present in alkene reactants. Ilie dimerization of acrylonitrile, for example, studied with cdeuterium labels in the c/5-l,2-dicyanocyclobutane products are given in structures (43), (44) and (45) an analogous set of three trans stereoisomers is formed. Recovered starting material shows partial loss of stereochemical integrity. 

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