Acetonitrile, oxide reaction with alkenes

Removal of the 0-substituted Fp group can be achieved by conversion into the cationic alkene-Fp complex using Ph3CPF6 and subsequent treatment with iodide, bromide or acetonitrile. Oxidative cleavage with ceric ammonium nitrate in methanol provides the methyl esters via carbon monoxide insertion followed by demetallation. The [3 + 2]-cydoaddition has been successfully applied to the synthesis of hydroazulenes (Scheme 1.11) [34]. This remarkable reaction takes advantage of the specific nucleophilic and electrophilic properties of V-allyl-, cationic t 5-dienyl-, cationic ri2-alkene- and ti4-diene-iron complexes, respectively. 

Formation of mixtures of the above type, which is common with internal olefins, do not occur with many functionalized alkenes. Thus, tertiary cinnamates and cinnamides undergo cycloadditions with benzonitrile oxides to give the 5-Ph and 4-Ph regioisomers in a 25-30 75-70 ratio. This result is in contrast to that obtained when methyl cinnamate was used as the dipolarophile (177). 1,3-Dipolar cycloaddition of nitrile oxides to ethyl o -hydroxycinnamate proceeds regiose-lectively to afford the corresponding ethyl fra s-3-aryl-4,5-dihydro-5-(2-hydro-xyphenyl)-4-isoxazolecarboxylates 36 (178). Reaction of 4-[( )-(2-ethoxycarbo-nylvinyl)] coumarin with acetonitrile oxide gives 37 (R = Me) and 38 in 73% and 3% yields, respectively, while reaction of the same dipolarophile with 4-methoxy-benzonitrile oxide affords only 37 (R = 4-MeOCr>H4) (85%) (179). 

The efficiency of a new chiral non-racemic and C2-symmetric 2,2-bipyridyl ligand (6) in copper(I)-catalysed asymmetric allylic oxidation reactions of the cyclic alkenes with f-butyl peroxybenzoate has been evaluated. On performing the reaction of cyclopentene, cyclohexene, and cycloheptene in acetonitrile the corresponding product, (lS)-cycloalk-2-enyl benzoate, was isolated in up to 69% yield and in 91% ee 29... 

If the reactions are carried out in a nitrile as solvent, rather than dichloromethane, using triflic acid as catalyst, a modified Ritter reaction takes place, and the intermediate nitrilium ion traps the liberated amine, forming an amidine (Scheme 67). In an earlier reaction cf. Scheme 67) the lithium perchlorate catalyzed reaction of sulfenyl chlorides with alkenes in the presence of nitriles had also given l-amido-2-sulfenyl adducts. Ritter products are also obtained in good yields by anodic oxidation (Pt or C, 1.2-1.4 V) of disulfides in acetonitrile, in the presence of excess alkene, using B114NBF4 as supporting electrolyte (Scheme 68). ... 

Quite recently, a new asymmetric addition reaction has been described by Tiecco. The oxidation of the diselenide 26 with ammonium persulfate produces the camphorselenyl sulfate, which reacts with alkenes in acetonitrile in the presence of water, to afford the hydroxyselenenylation products in good yields and with moderate to good diasteroselectivities [46b]. The results of these experiments are collected in Table 3. Moderate diastereomeric ratios were observed in the hydroxyselenenylation of cyclohexene, styrene and -methylstyrene. Good facial selectivity was observed in all the other cases. The two diastereomeric addition products thus obtained could be separated in most cases. Enantiomerically pure saturated or allylic alcohols... 

The addition of ZnBr2 to the tandem 1,3-azaprotio cyclotransfer-cycloaddition of a ketoxime with divinyl ketone results in rate enhancement and the exclusive formation of l-aza-7-oxabicyclo[3.2.1]octan-3-ones7 The 1,3-dipolar cycloaddition of 1-aza-l-cyclooctene 1-oxide with alkenes produces the corresponding isoxazolidines in high yields with a minimum of polymeric material. The cycloaddition of thiophene-2-carhaldehyde oxime with acetonitrile and methyl acrylate produces the 1,3-dipolar adduct, suhstituted isoxazolidines, and not the previously reported 4 - - 2-adducts. Density functional theory and semi-empirical methods have been used to investigate the 3 + 2-cycloaddition of azoxides with alkenes to produce 1,2,3-oxadiazolidines. The 3 -h 2-cycloaddition of a-nitrosostyrenes (62) with 1,3-diazabuta-1,3-dienes (63) and imines produces functionalized cyclic nitrones (64) regioselectively (Scheme 22). The first imequivocal 1,3-dipolar cycloaddition of sulfines involves the reaction of 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-oxide with diaryl thioketones to produce... 

Another ruthenium-catalyzed oxidation uses tetrapropylammonium permthenate (TRAP) [24]. Being a ruthenium(VII) oxide, the permthenate ion is a less powerful oxidant than rutheni-um(VIII) oxide and more functional groups are stable to the oxidation conditions, including alkenes, alkynes, amines, amides, benzyl, trityl and silyl ethers [24]. However, alcohols and lactols still undergo oxidations in high yield with W-methyl-morpholine A-oxide (NMO) as the stoichiometric oxidant. The reactions are usually carried out in dichloromethane, acetonitrile, or mixtures of both in the presence of molecular sieves [24]. 

Oxidation of the hydroxymalonic acid ene adducts with cerium(IV) ammonium nitrate in aqueous acetonitrile or sodium periodate results in oxidative didecarboxylation to give an allylcarboxylic acid. The two step process ene reaction with diethyl oxomalonate and oxidative didecarboxylation provides a general procedure for the conversion of alkenes to allylcarboxylic acids. 

Nitroacetamidation of conjugated dienes is efficient when a solution of nitronium tetrafluoroborate in acetonitrile obtained by anodic oxidation of dinitrogen tetroxide is used substantial amounts of both 1,2- and 1,4-adducts are usually obtained.34 Some conjugated nitroalkenes can be readily prepared by reaction of alkenes with sodium nitrite and iodine under mild conditions (Scheme 158).347... 

A key ingredient in the RuCl3/NaI04 oxidation appears to be the choice of solvent, with acetonitrile being preferred. Under these reaction conditions, alkenes such as 1-nonene are cleaved to acids (nonanoic acid, 89% yield)." Alcohols (see 332) can be oxidized to the acid (in this case forming 333 without disturbing the... 

We came to this area quite by chance. Our interest in nucleophilic functionalization of aromatics led us to consider photochemical reactions for this purpose. In several cases, such reactions involve ionization of the substrate. Furthermore, we were impressed by the work of Arnold and his co-workers showing that SET often occurs upon photoexcitation yielding an ion radical pair. In view of this fact, one of the experiments we carried out involved irradiation of the photochemical oxidant 1,4-naphthalenedicarbonitrile (DCN) in the presence of toluene and cyanide in deareated acetonitrile. Arnold s work had shown that cation radicals of alkenes add nucleophiles under this condition, and we wanted to test whether a similar reaction with... 

CAN-mediated nitration provides a convenient route for the introduction of a nitro group into a variety of substrates. Alkenes on treatment with an excess of sodium nitrite and CAN in chloroform under sonication afford nitroalkenes. When acetonitrile is used as the solvent, nitroacetamidation occurs in a Ritter-type fashion. However, the attempted nitroacetamidation of cyclo-pentene-1 -carboxaldehyde under similar conditions resulted in the formation of an unexpected dinitro-oxime compound. A one-pot synthesis of 3-acetyl- or 3-benzoylisoxazole derivatives by reaction of alkenes (or alkynes) with CAN in acetone or acetophenone has been reported. The proposed mechanism involves a-nitration of the solvent acetone, oxidation to generate the nitrile oxide, and subsequent 1,3-dipolar cycloaddition with alkenes or alkynes. The nitration of aromatic compounds such as carbozole, naphthalene, and coumarins by CAN has also been investigated. As an example, coumarin on treatment with 1 equiv of CAN in acetic acid gives 6-nitrocoumarin in 92% yield. ... 

It was also possible to set up a photocatalytic reaction where singlet oxygen oxidation of cyclic alkenes was controlled by the capsule via interaction with water-soluble Rose Bengal (RB) or insoluble dimethylbenzil (DMB) as sensitizers. All the alkenes provided quaternary 2 2 capsular self-assembled structures with the oxidation product distribution related to the position assumed in the cavity. The same reaction in acetonitrile without host led to a complex mixture of hydroperoxides (Figure 25). 

The addition of ozone (O3) to alkenes to give a primary ozonide (molozonide), which rearranges to an ozonide and eventually leads, on reduction, to carbonyl compounds (aldehydes and/or ketones), has already been mentioned and the reaction itself is shown in Scheme 6.11. However, it is important to recognize that this is only one example of a 4th- 2n electrocyclic addition and that orbital overlap for many sets of these reactions dictates their courses as well. Thus, to show the similarity of some of these dipolar 3 -f 2 addition reactions Equations 6.53-6.56 are provided. Although any alkene might be used as an example, (Z)-2-butene is used in each to emphasize that aU of them occur with retention of stereochemistry and, in the first (Equation 6.53), the reaction with ozone to form the primary ozonide (molozonide) is presented again (i.e., see Scheme 6.11). In a similar way, with a suitable azide, R-N3, readily prepared from an alkyl halide (Chapter 7), the same alkene forms a triazoline (Equation 6.54) and with nitrous oxide (N2O) the heterocycle (Chapter 13) cis -4,5-dimethyl-A -l,2,3-oxadiazoline (ds-4,5-dihydro-4,5-dimethyl-l,2,3-oxadiazole) (Equation 6.55). Finally, with a nitrile oxide, such as the oxide derived from ethanenitrile (acetonitrile [CH3ON]), the same alkene yields a different heterocycle, the dihydroisoxazole, 3,4,5-trimethyl-4,5-dihydroisoxazole (Equation 6.56). 

Oxalic and malonic acids, as well as a-hydroxy acids, easily react with cerium(IV) salts (Sheldon and Kochi, 1968). Simple alkanoic acids are much more resistant to attack by cerium(IV) salts. However, silver(I) salts catalyze the thermal decarboxylation of alkanoic acids by ammonium hexanitratocerate(IV) (Nagori et al., 1981). Cerium(IV) carboxylates can be decomposed by either a thermal or a photochemical reaction (Sheldon and Kochi, 1968). Alkyl radicals are released by the decarboxylation reaction, which yields alkanes, alkenes, esters and carbon dioxide. The oxidation of substituted benzilic acids by cerium(IV) salts affords the corresponding benzilic acids in quantitative yield (scheme 19) (Hanna and Sarac, 1977). Trahanovsky and coworkers reported that phenylacetic acid is decarboxylated by reaction with ammonium hexanitratocerate(IV) in aqueous acetonitrile containing nitric acid (Trahanovsky et al., 1974). The reaction products are benzyl alcohol, benzaldehyde, benzyl nitrate and carbon dioxide. The reaction is also applicable to substituted phenylacetic acids. The decarboxylation is a one-electron process and radicals are formed as intermediates. The rate-determining step is the decomposition of the phenylacetic acid/cerium(IV) complex into a benzyl radical and carbon dioxide. 

The synthesis of 2,3,5-trialkylpyrroles can be easily achieved by conjugate addition of nitroalkanes to 2-alken-l,4-dione (prepared by oxidative cleavage of 2,5-dialkylfuran) with DBU in acetonitrile, followed by chemoselective hydrogenation (10% Pd/C as catalyst) of the C-C- double bond of the enones obtained by elimination of HN02 from the Michael adduct. The Paal-Knorr reaction (Chapter 10) gives 2,3,5-trialkylpyrroles (Eq. 4.124).171... 

When the reaction of methyl 5,6-dideoxy-2,3-di-0-p-tolylsulfonyl-a-L-arafoino-hex-5-enofuranoside with silver nitrite and iodine was performed in more-polar solvents, such as methanol and acetonitrile, a /3-iodo nitrate was produced, in addition to the C-iodo-C-nitro adduct 88 in methanol, the ratio of the two products was130 3 2. The /3-iodo nitrate was identical with the adduct obtained by the reaction of the alkene with silver nitrate and iodine in acetonitrile.132 The formation of the /3-iodo nitrate in the silver nitrite-iodine reaction in polar solvents may be due to the increased solubility of the silver nitrite the available nitrite ions could then be oxidized to nitrates. The positions of the iodo and nitrate groups in the adduct have not yet been established. 

Iodine-catalysed hydroperoxidation of cyclic and acyclic ketones with aqueous hydrogen peroxide in acetonitrile is an efficient and eco-friendly method for the synthesis of gem -dihydroperoxides and the reaction is conducted in a neutral medium with a readily available low-cost oxidant and catalyst.218 Aryl benzyl selenoxides, particularly benzyl 3,5-bis(trifluoromethyl)phenyl selenoxide, are excellent catalysts for the epoxidation of alkenes and Baeyer-Villiger oxidation of aldehydes and ketones with hydrogen peroxide.219 Efficient, eco-friendly, and selective oxidation of secondary alcohols is achieved with hydrogen peroxide using aqueous hydrogen bromide as a catalyst. Other peroxides such as i-butyl hydroperoxide (TBHP), sodium... 

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