Mesitonitrile oxide cycloaddition reactions

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). 

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). 

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. 

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>. 

The reaction of the dithioxo compound (6) with A -aryl-C-ethoxycarbonylnitrilimines (8) led to the l,2,4-triazino-[4,3-(f]-l,2,4-triazepine (10) via the 1,3-dipolar cycloadduct (9) <92BSB977>. Treatment of 2,7-dimethyl-3,5-dimethylthio-l,2,4-triazepine (7) with mesitonitrile oxide in aqueous medium resulted in peri- and regioselective cycloaddition, giving rise to the isoxazolo[5,4-e]-1,2,4-triazepine (12) (80% yield) via the cycloadduct (11). The cycloaddition of dichlorocarbene to (7) also proceeded to form the azirino[2,l- ]-l,2,4-triazepine (13) <85RTC129>. 

The fused oxazole derivative 100 was synthesized from 3-azido-3-deoxy-l,2 5,6-di-O-isopropylidene-a-D-allofuranose, the key final step being the reaction of methyl 3-amino-3-deoxy-5,6-0-isopropylidene-p-D-alloside with DMF dimethyl acetal. The annelated pyranoside 101 was obtained by cyclization of a branched chain hexosulose derivative, and the fused triazole-piperidinoses such as 102 were made by a radical cyclization of a 3-pyrazolo-6-iodo-sugar derivative. The spiro-isoxazohne 103 and related isomers have been synthesized by dipolar cycloadditions of mesitonitrile oxide to 2-deoxy-2-C-methyl-ene-pentonic acids, themselves available in five steps from D-mannitol. Intra-... 

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