Maleic anhydride, reaction with nitronic

The reactions of A-phenyl a-r-butyl nitrone (PEN) with maleimides, maleic anhydride, and diethyl maleate have been studied by EPR and two types of spin adduct detected. They arise from the reductive addition of PEN to the alkenes and the degradation product of DEN (2-methyl-2-nitropropane). The deuterium and muonium kinetic isotope effects for the addition of the hydrogen atom to a variety of alkenes have been determined experimentally and theoretically. ... 

The reaction of nitrone 101 with cyclic olefins, such as maleic anhydride.61 W-phenylmaleimide,77 cyclopentene,77 norbornene,77 in-dene.77 and acenaphthylene,77 is normal and gives isoxazolidine of type V. Some reactions of a-(6-uracilyl) jV-phenylnitrone are also reported those with allyl alcohol, methyl acrylate, acrylamide, and styrenes, all give 5 substituted 3-uracilylisoxazolidines (type I).79,80 With methyl methacrylate a type III cycloadduct was formed.79,80... 

The reactions with various cyclic olefins are also described. The products have structures similar to those from other nitrones. With maleic anhydride,47 tV-phenylmaleimide,47 norbornene,7,39 nor-bornadiene,39 indene,48 dimethyl bicyclo[2.2.1]hept-2-ene-5,6-... 

Since the discovery of the very remarkable 100% endo selectivity of the reactions of nitronic esters with dimethyl maleate, maleic anhydride and maleimides secondary orbital interactions involving the nitrogen atom of the 1,3-dipole and the substituents on the dipolarophile have been postulated as strong endo-orienting factors, able to overwhelm the contrasting steric factors (Figure 1). 

Allenes also undergo [3-1-2] cycloaddition reactions with diazo compounds and nitrones and [4-1-2] cycloaddition reactions with diolefins. In the latter reaction, allenes act as dienophiles. In the case of allenes with attached double bonds, such as divinylallene, one of the allene double bonds participates in the Diels-Alder reaction. In the reaction of divinylallene 1 with maleic anhydride at 65 °C in benzene a monoadduct 2 is formed. 

However, at least one example is known of acetylated nitronic acids 9 (Scheme 8.3) supposed to react directly with a dipolarophile (dimethyl acetylenedicarboxylate) to give the expected isoxazole derivatives 11 via the unstable intermediate adducts 10 (R = Ph) rather than via nitrile oxides. In fact, isolated 9 (R = Ph), in standard reaction conditions but in the absence of dipolarophile, decomposed to benzoic acid, with no diphenylfuroxan being detected [30]. Notice that this result refers only to the mentioned dipolarophile, whereas attempted reaction with other dipolarophiles (maleic anhydride or diphenylacetylene) failed. 

The applicability of thioketones in the synthesis of heterocyclic compounds has been further demonstrated. The Diels-Alder reaction of thiobenzophenone with l,3>5-cycloheptatriene gave the (2 + 4) cycloadduct (101) in 40% yield. Cycloheptatrienethione (92) yielded the (8 + 2) cycloadduct (102) quantitatively by reaction with maleic anhydride, and the bicyclic compound (103) in 65% yield by reaction with dimethyl acetylenedicarboxylate. Compound (103) was considered to be a rearrangement product of the probably primarily formed (8 + 2) cycloadduct intermediate (104). " The in situ addition of nitrile oxides to aromatic thioketones resulted in formation of 1,4,2-oxathiazoles, " whereas 1,4,2-oxathiazolidines were the products in the reactions of some alicyclic thiones with nitrones. The formation of thio-ozonides (1,2,4-trithiolans) by treatment of thioketones with amines or chloramine T was investigated recently. ... 

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