Unsaturated esters nitration

Because nitration of alkenes with nitronium salts proceeds via carbocation intermediates, nitration of electron-deficient alkenes with nitronium salts is rare. Only a few cases are reported. The reaction of a,(3-unsaturated esters with nitronium salts affords products via highly reactive ot-carbonyl cations.75... 

Conversion of ketone 80 to the enol silane followed by addition of lithium aluminum hydride to the reaction mixture directly provides the allylic alcohol 81 [70]. Treatment of crude allylic alcohol 81 with tert-butyldimethylsilyl chloride followed by N-b ro m o s u cc i n i m i de furnishes the a-bromoketone 82 in 84 % yield over the two-step sequence from a.p-unsaturated ester 80. Finally, a one-pot Komblum oxidation [71] of a-bromoketone 82 is achieved by way of the nitrate ester to deliver the glyoxal 71. It is worth noting that the sequence to glyoxal 71 requires only a single chromatographic purification at the second to last step (Scheme 5.10). 

Thus, the N,N-dibenzyl-protected aminonitrile 55 was prepared via Swern oxidation of N,N-dibenzylaminoethanol 54 followed by treatment with the enantio-pure amine auxiliary (S,S)-53 and HCN, resulting in the formation of a 3 2 epimeric mixture of the aminonitriles 55 in 55% yield, from which the single dia-stereomers could be isolated by chromatography. After lithiation with LDA, addition to the requisite (E)-a, P-unsaturated esters and hydrolysis of the aminonitrile moiety with silver nitrate, the desired a-amino keto esters R)-S6 were obtained with yields of 65-81% and enantiomeric excesses ee of 78-98%, which could be improved to ee > 98% by a simple recrystallization. Since the amino ketone functionality can be cleaved oxidatively, the 5-amino-4-oxo-esters 56 could be transformed to the corresponding succinic half-esters 57 with hydrogen peroxide in methanol in good to excellent yields (68-90%) (Scheme 1.1.15). 

It was found that the 15-membered macrocyclic complexes were significantly less acidic. Similar reversible protonations have been shown to occur in related macrocyclic complexes36 37 and this work has been developed by Busch into a major study of ligand reactions,38 which are summarized in equations (16)—(19). It is significant that these reactions include not only typical substitution reactions such as acylation and nitration (equations 16 and 19), but also nucleophilic addition to isocyanates (equation 17) and to a, 3-unsaturated esters (equation 18). 

The deacylated Jager-type complexes (62) can be reacylated with a variety of groups and also undergo nitration and addition to isocyanates and a,p unsaturated esters (Scheme 23).139,140... 

Reaction intermediates formed in the nitration of a series of a,/f-unsaturated esters, such as (47), with NO2BF4 have been reported to exhibit the expected behaviour of a-carbonyl cations. Three diagnostic reaction types were observed (1) Ritter reaction (2) cyclopropane formation from propyl cations (3) Wagner-Meerwein migration of alkyl groups. Semi-empirical calculations of the relative gas-phase stabilities of the proposed intermediate cations have also been performed.53... 

Cerium(IV) ammonium nitrate (CAN) has been reported to catalyse a facile and efficient aza-Michael addition of aromatic and aliphatic amines to a -unsaturated esters in the absence of solvent under ultrasound irradiation.136 a,/l-Unsaturated ketones react in aqueous solutions under these conditions but only with aliphatic (not aromatic) amines.137... 

Monocarboxylic esters were further separated by argentation TLC [silica GF254 impregnated with 5% (w/v) silver nitrate] into saturated esters (Rf = 0.51), monounsaturated esters (R = 0.42), diunsaturated esters (Rf = 0.29), and poly unsaturated esters (Rf < 0.29) by development in n-heptane-diethyl ether-methanol (90 10 1, v/v/v) (19). 

An alternate procedure involves the precipitation of mixed copper and chromium hydroxides from a solution of chromium nitrate and copper nitrate by the addition of an sodium bicarbonate and then heating the precipitate to 300°-500°C.30 In this procedure, the copperchromium ratio can be varied over a wide range. A ratio between four and eight was optimum for use in the hydrogenation of esters to alcohols (Eqn. 13.6).30 A related Zn-CrO catalyst prepared by the decomposition of precipitated zinc-copper hydroxides was effective in the hydrogenation of unsaturated esters to unsaturated alcohols (Eqn. 13.7). 0 The presence of a small amount of alumina increased catalyst activity and selectivity. Some of these catalysts, however, tend to become colloidal on use so they can present separation problems. O... 

By Addition to Unsaturated Substrates. Bromo- and iodo-functionalization of alkenes using a combination of the halogen and a mercury(II) salt has enabled the preparation of a series of 1,2-disubstituted products in which the second substituent, derived from the mercury salt, may be another halide or a series of other groups including esters, nitrate, thiocyanide, or a sulphone. Stereoselective bromination of acetylenes to furnish... 

The elution characteristics of a wide variety of unsaturated esters have been studied. For example, the complete series of methyl cis- and trans-octadecenoates [323] and methylene-interrupted c s,c s-octadecadienoates [157] have been subjected to silver nitrate TLC. When run in order on a single TLC plate, each series migrates in the form of a sinusoidal curve similar to that observed with isomeric polar esters on silica gel alone (see below), with a minimum at the 6-18 1 isomer (or at 6,9-18 2 in the case of the dienes) and a maximum at the 13-18 1 isomer, frans-lsomers migrate consistently ahead of the corresponding c s-isomers, with the... 

The enantiomeric reduction of 2-nitro-l-phenylprop-l-ene has been studied in a range of Gram-positive organisms including strains of Rhodococcus rhodochrous (Sakai et al. 1985). The enantiomeric purity of the product depended on the strain used, the length of cultivation, and the maintenance of a low pH that is consistent with the later results of Meah and Massey (2000). It has been shown that an NADPH-linked reduction of a,p-unsaturated nitro compounds may also be accomplished by old yellow enzyme via the flcf-nitro form (Meah and Massey 2000). This is formally analogous to the reduction and dismutation of cyclic enones by the same enzyme (Vaz et al. 1995), and the reductive fission of nitrate esters by an enzyme homologous to the old yellow enzyme from Saccharomyces cerevisiae (Snape et al. 1997). 

The reaction of fuming nitric acid with 2-methyl-2-butene (3) is reported to yield 2-methyl-3-nitro-2-butene (4). The reaction of alkenes with fuming nitric acid, either neat or in chlorinated solvents, is an important route to unsaturated nitrosteroids, which assumedly arise from the dehydration of /3-nitroalcohols or the elimination of nitric acid from /3-nitro-nitrate esters. Temperature control in these reactions is important if an excess of oxidation by-products is to be avoided. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Based on our previous results on the nucleophilic alkenoylation of aldehydes via metallated a, 3-unsaturated aminonitriles [50], we now envisaged an enanti-oselective variant. Thus, the enantiopure a-aminonitriles 60 were metallated with LDA and by reaction with aldehydes the adducts 61 could be obtained. Subsequent cleavage of the aminonitrile function with silver nitrate led to the desired a -hydroxyenones 62 in overall yields of 29-80% and enantiomeric excesses ee of 50-69%. Alternatively, the conjugate addition of the lithiated aminonitrile 63 to t-butyl crotonate led to the y-keto ester 63 in 35% yield and an enantiomeric excess ee of >90% (Scheme 1.1.18). 

It has been reported by Cauquil and Barrera 83 that treatment of Oyclohexene oxide with two molar equivalents of silver perchlorate leads to the formation of metallic silver and a diperchlorate enter formulated as shown in Eq. <431). Similar unsaturated dinitrate esters, which are extremely explosive, wen reported to be formed with silver nitrate.2 8... 

Natural products and transformed natural products can also be used as binding agents for packaging applications. These are shellac, dammar gum, dried unsaturated oils (linseed oil), rosin and hydrated esters of rosin, cellulose acetate and propionate acetate, cellulose acetobutyrate, cellulose nitrate and ethyl cellulose. 

To further the identification of the minor fatty acids in evening primrose oil, methyl esters of fatty acids were separated by column chromatography on a silver nitrate-silicic acid absorbent according to their degree of unsaturation (De Vries, 1963). The data obtained are summarized in Table 4.4 based on identification by gas chromatography-mass spectrometry. Of the saturated fatty acids, C13 0, C19 0, C21 0 and C23 0 had not been reported previously. A number of monounsaturated fatty acids have been reported previously in EPO... 

---