THE REACTIONS OF NITROGEN-DIOXIDE WITH DIENES

The reaction of nitrogen dioxide with conjugated dienes (2,5-dimethylh exa-2,4-diene, hexa-2,4-diene and 2,3-dimethylbuta-1,3-diene) in organ ic solvents (mainly hexane, benzene and diethyl ether) results mainly in 1,4-addition giving, with the first two substrates, a mixture of 1, 4-dinitro compounds and 1,4-nitro alcohols. The latter are presumably formed from hydrolysis of the intermediate nitronitrites. With 2,3-dim ethylbuta-1,3-diene, only the cis and trans 1,4-dinitro compounds were isolated. The reactions effectively stop after the addition of two ni trogen dioxide radicals, only traces of tetrasubstituted products bein g obtained. With the unconjugated hepta-1,6-diene, addition can be mad e to occur to both double bonds but, when two equivalents of nitrogen dioxide are added very slowly, the main products derive from addition to one double bond and cyclisation to form cis and trans 1,2-bis(nitro methyl)cyclopentane. All the above reactions give a very complex mixtu re of products and the product composition depends markedly on the rea ction conditions; however, with the conjugated dienes, the 1,4-dinitro compounds can be obtained in yields-of ca. 50%. The crystal Structure of trans-1,4-dinitro-2,3-dimethylbut-2-ene was determined.