Nitrile oxides, reaction with benzoquinones

An unusual solvent effect was observed in cycloadditions of aromatic nitrile N-oxides with alkyl-substituted p-benzoquinones in ethanol-water (60 40) the reaction rates were 14-fold greater than those in chloroform (148). The use of ion pairs to control nitrile oxide cycloadditions was demonstrated. A chiral auxiliary bearing an ionic group and an associated counterion provides enhanced selectivity in the cycloaddition the intramolecular salt effect controls the orientation of the... 

I.3.4.2. Intermolecular Cycloaddition at C=X or X=Y Bonds Cycloaddition reactions of nitrile oxides to double bonds containing heteroatoms are well documented. In particular, there are several reviews concerning problems both of general (289) and individual aspects. They cover reactions of nitrile oxides with cumulene structures (290), stereo- and regiocontrol of 1,3-dipolar cycloadditions of imines and nitrile oxides by metal ions (291), cycloaddition reactions of o-benzoquinones (292, 293) and aromatic seleno aldehydes as dipolarophiles in reactions with nitrile oxides (294). 

A synthesis of novel spirodioxazole systems by the 1,3-dipolar cycloaddition reactions of 3,5-di-ferf-butyl-1,2-benzoquinone with aromatic nitrile oxides has been described (Scheme 1.31). Though yields are high (80%-100%), the regios-electivity is low, the regioisomer ratio 181 182 being dependent on the Ar nature (349). 

Polymethyl 3a,4,7,7a-tetrahydroindoxazenes (77) are obtained by thermal rearrangement of the benzonitrile oxide-hexamethyl-Dewar-benzene cycloadducts (76).90 Reaction of 2,4,6-trimethylbenzonitrile oxide with 3,6-dimethyl-p-benzoquinone yields the 4,7-dioxo-3a,4,7,7a-tetrahydroin-doxazene78(Ar = 2,4,6-Me3C6H2) or its regioisomer, and addition proceeds similarly with 2,6-dimethyl-p-benzoquinone. In a number of other examples, nitrile oxides were found to cycloadd to the C=0 bond of quinones.91... 

It has been demonstrated that N-hydroxytryptophan can be converted to /3-carbolines in two ways (Fig. 41). Pictet-Spengler reaction of 1 with acetals provided the N -hydroxytetrahydro-/8-carbolines (2) (287). A modified Bischler-Napieralski reaction of 1 with trimethylorthoformate gave N -0X0-3,4-dihydro-/3-carbolines (3), the nitrone function of which can undergo 1,3-dipolar cycloaddition with alkenes (288) and nitriles (289), providing isoxazolidine (4) and dehydro-1,2,4-oxadiazoline (5), annulated TBCs, respectively. Nitrone 3 also was obtained by oxidation of the N-hydroxy-j8-carboline 2 with 2,3-dichloro-5,6-dicyano-l, 4-benzoquinone (DDQ). N-Oxygenated TBCs showed no affinity for the benzodiazepine and tryptamine receptors (290). Unfortunately, no toxicity data were recorded for these substituted hydroxylamines. 

The reaction of the cationic polyether, 196, with sodium cyanide led to the isolation of the neutral adduct, 197.254 Demetallation of these adducts via chemical oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) gave the nitrile functionalized polyaromatic ethers 198 (Scheme 2.52). 

The results of an IR and chemical analysis of some rubbers cured with chloranil (tetrachloro-p-benzoquinone) are discussed. The compounds tested consisted of 10 pts. Chloranil and 0-5 pts. Zinc oxide to 100 pts. Rubber(cis-1,4-polybutadiene, sodium butadiene rubber and nitrile rubber). It is shown that, during curing, dehydrogenation is accompanied by addition of chloranil to the polymer molecules by a diels-alder and other reactions. 9 refs. Accession no. 15599... 

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