Naphthoquinones Nitriles

Naphthoquinone, ketone-alcohol reduction, diastereoselectivity, 76-77 Nitrile reduction, a,/3-unsaturated nitriles, 96... 

Side reactions that occur with intramolecular cycloaddition, such as linear oligomerization or dimerization of the nitrile oxide, are not very common when shorter chain lengths n < 1) are used due to the entropically favored intramolecular process. A rather unusual result in this regard involves the formation of a fused cyclooctane instead of the less-strained six-membered ring (also fused) in the cycloaddition of the nitrile oxide derived from p-naphthoquinone (Scheme 6.43). This result is consistent with the effect of electron-withdrawal in the enedione part, leading to increased reactivity (247), and also reflects the known sluggishness of cyclohexenes towards nitrile oxides (cf. Section 6.2.1.2). 

Domino [3+2] cycloaddition/annulation reactions of aminophenyl-ynones 23 with nitrile oxides, generated in situ from chloro oximes 22, allowed the synthesis of isoxazolo[4,5-c]quinolines 24, in satisfactory yields <03EJO1423>. Bromine substituents on naphthoquinones activate and orient 1,3-DC with nitrile oxides. Compound 25 reacted with halo oximes 22 to give regioselectively only unsymmetrical naphthoquinones 26, as polyketide building blocks <03TL8901>. 

The photochemical generation and reactions of nitrile ylides have again been studied. Irradiation of azirine (55) in the presence of 1,4-naphthoquinone (56) gave the isoindoledione (57) via 1,3-dipolar addition of the transient nitrile ylide (SS)."" The kinetics of the reactions of nitrile ylides with electron-poor alkenes have been determined, with evidence being reported for the formation... 

Usually 5 drops of a 0.2% alcoholic malonic nitrile solution and 5 drops of a 0.3% alcoholic solution of a-naphthoquinone are added to 5 c.c. of the solution being studied. Both reacting solutions remain unaltered for a long period. Their volumes should be measured carefully, the use of a micro burette being recommended in certain cases. The range of applicability is pH 4.5-11.5. 

As mentioned earlier, the TMM-Pd procedure for [3 + 2] cycloadditions is selective for electron-deficient olefins, where the electron-withdrawing group may be a ketone, ester, nitrile or sulfone. However, not all electron-deficient olefins will undergo the cycloaddition. For example, 1,4-naphthoquinone, chloracrylonitrile and tetracyanoethylene do not give adducts under the palladium-catalyzed conditions. 

Naphthoquinones (xee Quinones) NmmJES (see also Amino niinles. Cyanohydrins, Hydroxy nitriles)... 

Keywords Bioorthogonal reaction Photo-triggered reaction Photoclick Tetrazole Nitrile imine Azirine Cyclopropenone o-Naphthoquinone methide o-Quinodimethanes Hetero Diels-Alder reaction... 

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