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 1a-f 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 2. The process exclusively produces diastereomeric mixtures of a chiral d,1 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 derivatives, the resulting vinylcyclopropanes 3 can be cyclopropanated with excess diazomethane to give the same diastereomeric mixtures as obtained by direct bis(cyclopropanation) of 1. ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).