Mesitonitrile oxide cycloaddition

The 1,3-dipolar cycloaddition of mesitonitrile oxide 575 to benzo[h]thiophene S-oxides 576 in non-stereoselective and both syn and anti adducts 577 are obtained674,675 (equation 366). 

Better yields were obtained with the stable mesitonitrile oxide (343) which enables the cycloaddition at higher temperature (entry 3). In the reaction of 341... 

Methylmagnesium bromide (191) exerts a great influence on the stereoselectivity of the reactions between mesitonitrile oxide 10 and the Baylis-Hillman adducts 192. In the absence of a Grignard reagent, a mixture of isomers is formed in which compounds 194 are the main products. The presence of a Grignard reagent reverses the stereoselectivity (Scheme 9.59). When Fisera [107] performed these reactions under microwave irradiation, the reaction times decreased from days to less than 5 min without any loss of stereoselectivity for noncatalyzed cycloadditions, but with a small change in the stereoselectivity in the chelated reactions. 

Dipolar cycloaddition reactions occur with mesitonitrile oxide and tellones to afford oxatellurazole in good yield,25,245,248 while a triazene is formed with phenyl azide25 probably via detelluration of a telluratriazoline ring (Scheme 44). 

There are a few communications concerning cycloadditions of nitrile oxides to unsaturated oxa and aza cage systems. Benzo- and mesitonitrile oxides RCNO give, with five substituted 7-oxanorbomenes 106, mixtures of the corresponding exo-adducts 107 and 108 in nearly quantitative yields. No traces of compounds resulting from the endo-face attack was detected (274). Substituents at positions 5 and 6 of 106 render the process highly regioselective. 

Reactions of 2,3-dihydro-17/-1,4-diazepines with mesitonitrile oxide proceed with site- and regiospecific 1,3-dipolar cycloaddition leading to bis[ 1,2,4] oxadiazolo[l,4]diazepine derivatives 160 (326). Of the three compounds 160 only the one with R = R = Ph is formed with trails arranged substituents. The two other products (R = R = Me and R = Me, R = Ph) are mixtures of diastereoiso-mers. The heterotricyclic 6,1 Oa, 11,11 a-tetrahydro-5//-bis[ 1,2,4]oxadiazolo[4,5-d 5 -g][, A diiazeipm.e structure 160 of the obtained bis-adducts indicates that the hetero double bonds are much more reactive than the olefinic ones. No evidence for the formation of monoadducts was obtained. 

Benzonitrile oxide and mesitonitrile oxide undergo 1,3-dipolar cycloaddition reactions with 1,3,5-triphosphinines under mild conditions to afford fused heterocyclic compounds (Scheme 1.33), for example, 192 and 193. Oxaphosphazoles and oxadiphospholes have become accessible by thermal fragmentation reactions of such fused heterocyclic compounds (358). 

Kinetically stabilized germanothiones Tbt(Tip)Ge = S, Tbt(Dis)Ge = S and germanoselones Tbt(Tip)Ge = Se, Tbt(Dis)Ge = Se [Dis = bis(trimethylsilyl) methyl, Tbt = 2,4,6-trisbis(trimethylsilyl)methylphenyl, Tip = 2,4,6-tris(iso-propyl)phenyl], have been synthesized and have shown to enter 1,3-dipolar cycloaddition reactions with mesitonitrile oxide (361). 

Electroactive 3-(N-phenylpyrazolyl)fullereno[l,2-r/]isoxazolines have been synthesized by using 1,3-dipolar cycloaddition of pyrazole nitrile oxides, generated in situ, to Cgo at elevated temperature or microwave irradiation. The cyclic voltammetry measurements show a strong donor pyrazole ring, and a better acceptor ability of the fullerene moiety than the parent C60 (538). Treating fullerene Cgo with mesitonitrile oxide in toluene gives fullerene-nitrile oxide adduct, which is supposed to be useful for electrical and optical components (539). 

Like their stable heavy ketone congeners, the germanetellones Tbt(R)Ge = Te underwent [2 + 3] and [2 + 4] cycloadditions with mesitonitrile oxide and 2,3-dimethyl-l, 3-butadiene, respectively144 (Scheme 39). 

A study of the regioselectivity of the 1,3-dipolar cycloaddition of aliphatic nitrile oxides with cinnamic acid esters has been published. AMI MO studies on the gas-phase 1,3-dipolar cycloaddition of 1,2,4-triazepine and formonitrile oxide show that the mechanism leading to the most stable adduct is concerted. An ab initio study of the regiochemistry of 1,3-dipolar cycloadditions of diazomethane and formonitrile oxide with ethene, propene, and methyl vinyl ether has been presented. The 1,3-dipolar cycloaddition of mesitonitrile oxide with 4,7-phenanthroline yields both mono-and bis-adducts. Alkynyl(phenyl)iodonium triflates undergo 2 - - 3-cycloaddition with ethyl diazoacetate, Ai-f-butyl-a-phenyl nitrone and f-butyl nitrile oxide to produce substituted pyrroles, dihydroisoxazoles, and isoxazoles respectively." 2/3-Vinyl-franwoctahydro-l,3-benzoxazine (43) undergoes 1,3-dipolar cycloaddition with nitrile oxides with high diastereoselectivity (90% de) (Scheme IS)." " ... 

Tetrathiametallolanes (343) <94PS(95-96)2i> are useful precursors of analogues of thio-ketones (343) which act as dipolarophiles in (3 + 2)-cycloaddition reactions to give, for example, (400) with mesitonitrile oxide. 

Enamines are known to undergo cycloaddition with nitrile oxides. However, 3-pyrrolidinothiophene with mesitonitrile oxide gave only the oxime (289) no isoxazoline could be detected (74RTC321). Whether an isoxazoline is an intermediate in the formation... 

The first example of a [2 + 4] cycloaddition of a thiophene 1-oxide seems to be the formation of a 1 1 mixture of the syn and anti isomers of 3-(2,4,6-trimethylphenyl)-8b-methylbenzo[6]thieno[2,3-mesitonitrile oxide with 3-methyIbenzo[6]thiophene 1-oxide (Scheme 190) (79TL4845). The cycloaddition seems to be regioselective. 

Nitrile oxides react with the methyl enol ethers of (Rs)-l -fluoro-alkyl-2-(p-tolylsulfinyl)ethanones to produce (45,5/f,/fs)-4,5-dihydroisoxazoles with high regio-and diastereo-selectivity.87 In the 1,3-dipolar cycloaddition of benzonitrile oxide with adamantane-2-thiones and 2-methyleneadamantanes, the favoured approach is syn, as predicted by the Cieplak s transition-state hyperconjugation model.88 The 1,3-dipolar cycloaddition reaction of acetonitrile oxide with bicyclo[2.2.l]hepta-2,5-diene yields two 1 1 adducts and four of six possible 2 1 adducts.89 Moderate catalytic efficiency, ligand acceleration effect, and concentration effect have been observed in the magnesium ion-mediated 1,3-dipolar cycloadditions of stable mesitonitrile oxide to allylic alcohols.90 The cycloaddition reactions of acryloyl derivatives of the Rebek imide benzoxazole with nitrile oxides are very stereoselective but show reaction rates and regioselectivities comparable to simple achiral models.91. 

As an alternative to [3+2] cycloaddition, product 191 (X = Se) can be prepared in 90% yield using a [4+2] cycloreversion reaction of the six-membered heterocycle 206 in the presence of mesitonitrile oxide (Equation 22) <1999JA8811>. 

The silylene 153, which exists in an equilibrium with the corresponding dimer in solution, underwent a [3+1] cycloaddition reaction with mesitonitrile oxide to afford l-oxa-2-aza-4-silete 154 (Scheme 59). The latter compound is unstable and its presence in the reaction mixture was established only by means of H NMR spectroscopy <2006JOM(691)1341>. 

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