From 3,4-dinitrothiophene to nitrocyclopropanes and 1,1'-dinitro-1,1'-bi(cyclopropyl) compounds

Treatment of (E,E)-1,4-diaryl-2,3-dinitro-1,3-butadienes (I) with diazomethane in Et2O or THF represents a facile and high-yielding route to 2,2'-diaryl-1,1'-dinitro-1,1'-bi(cyclopropyl)s. The process exclusively produces diastereomeric mixts. of a chiral d,l pair and a meso form, the relative percentages of which depend on the aryl moiety, consistently with a concerted syn-stereoselective cyclopropanation of each double bond. With 1 mol-equiv of CH2N2, the cyclopropanation can effectively be limited to one double bond of the starting dinitrobutadiene, thus allowing a synthetically useful differentiation between the two originally conjugated nitrovinyl moieties. As verified with model derivs., the resulting vinylcyclopropanes can be cyclopropanated with excess diazomethane to give the same diastereomeric mixts. as obtained by direct bis(cyclopropanation) of I