Radical anions were generated by reduction of aliphatic diazenes with sodium-potassium alloy combined with U.V. irradiation (primary alkyl azo compounds), sodium-potassium alloy (secondary and tertiary alkyl azo compounds) and with crotylpotassium combined with U.V. irradiation (primary, secondary, and tertiary alkyl azo compounds); nitrogen hyperfine coupling constants range from 0.775 to 0.883 mT.
The preparation of methyl-substituted 1,2-dimethylenecyclopentanes and their reactivity in (4 + 2) cycloadditions with a,&un-saturated carboxylic esters and nitriles is studied. In kinetic measurements the methyl groups show a moderately rate-enhancing effect. The results are compared with those for analogously substituted butadienes. Whereas 1,ldimethylbutadiene reacts with TCNE to form a mixture of(2 + 2) and (4 + 2) cycloadducts, the correspondingly substituted 1Jdimethylenecyciopentane gives only the (4 + 2) adduct.
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