Polynitro-Substituted Strained-Ring Compounds. Synthesis, Mechanism of Formation, and Structure of trans-Dinitrocyclopropanes

Article abstract of DOI:10.1021/ja00252a023

1,2-Dinitrocyclopropane, 1,2-dimethyl-1,2-dinitrocyclopropane, and 1,2-diethyl-1,2-dinitrocyclopropane have been prepared in 23-36percent yield by oxidative cyclization of the corresponding open-chain 1,3-dinitronate dianions with iodide in DMSO.In each case only the trans isomer of the dinitrocyclopropane was obtained.Treatment of 2,4-dibromo-2,4-dinitropentane with the lithium salt of 2-nitropropane gave trans-1,2-dimethyl-1,2-dinitrocyclopropane, suggesting the intermediacy of a halonitro nitronate intermediate in the oxidative cyclization process.Further mechanistic studies using m-dinitrobenzene suggest either an internal single-electron transfer, nonchain pathway or an internal S_N2 process leading to the dinitrocyclopropanes.An X-ray crystallographic study performed on trans-1,2-dinitrocyclopropane indicates substantially shortened distal C-C bonds (1.47 Angstroem) and bisected conformations for each nitro group.Ab initio calculations using a 4-31G basis set are in agreement with the X-ray data, except longer distal C-C bonds (1.49 Angstroem) are calculated.Ab initio calculations using a variety of basis sets were performed on nitrocyclopropane as a model.