Olefin Reactions of Mechanistic Interest

Oxidation of benzil bisphenylhydrazone gave (529), which gives 1 1 cycloadducts, e.g. (530), with a variety of acetylenic and olefinic dipolaro-philes.  

An explanation using simple perturbation theory has been offered for the as yet unresolved question of regioselectivity in 1,3-dipolar cycloadditions to olefins for the particular case of diazonium betaines. This question of orientation or regioselectivity is also taken up by Firestone, whose conclusions are that the facts are better explained using his biradical interpretation of 1,3-cycloadditions.  

Methoxycarbonylsulphamoyl chloride (531) reacts with sodium hydride at —78 C in THF to give the salt (532), which produces the inner salt (533) on treatment with triethylamine. At 30 °C, (532) decomposes to yield a solvent-complexed methyl A -sulphonylurethane which cycloadds stereospecifically with substituted alkenes to give thiazetidines (534) and oxathiazines (535). A 

Intramolecular cycloaddition of 5-allylcyclohexa-1,3-diene leads to tricyclo[3,3,l,0 ]non-3-ene on heating at 193°C. Examination by n.m.r. of the products from an appropriately deuterium-labelled starting material shows that the product (541) is derived almost exclusively by the [4-1-2] rather than the [2 -I- 2] (542) mode or by a biradical mechanism. At higher temperature at least one other pathway intervenes to scramble the label 

An intramolecular Diels-Alder reaction has been extended to the preparation of substituted isoindolines (543) eind the thermodynamic parameters for the reaction have been evaluated. The mechanism of the Diels-Alder 

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