Substitution reactions of nitrothiophens. V. Isolation and reactions of the exocyclic methylene intermediates in SN(AEAE) reactions

Abstract

The reaction of lithium 2-nitropropan-2-ide(1)with 2-(1'-chloro-2',2'-dimethylpropyl)-4-nitrothiophen (5) gives a complex mixture of products, including the salt (15), nitro compounds (17a-c)and oximes (18) and (19). The formation of these products can be rationalized in terms of initial formation of 5-[(Z)-2',2'-dimethylpropylidene]-2-(1''-methyl-1''-nitroethyl)-3-nitro-2,5-dihydrothiophen (16) whose analogues have been proposed as reactive intermediates in the S_N(AEAE) reaction. The diene (16), which is a stable isolable compound [tautomeric with the thiophen (27)], reacts with the salt (1) to give the above products and with sodium p-toluenesulfinate to give the sulfone(32). The analogous chloride (6) and the acetate (7) react in a similar fashion and give the diene (21), which also reacts in part in an S_N(AEAE) reaction to give the substitution product (23).