DIPOLAR SPIROCYCLIC SIGMA-COMPLEXES BASED ON OF 4,6-DINITROBENZOFUROXAN

The first dipolar spiro-sigma-complexes with a superelectrophilic dini ntrobenzofuroxan fragment and tropolone systems with diastereotopic su bstituents were synthesized. The kinetics of their enantiotopomerizati on, which occurs via cleavage-formation of the C-spiro-heteroatom bond , was studied by dynamic H-1 NMR. The stereorigidity of dinitrobenzofu roxan spiro-complexes in this degenerated process increases in the ser ies: tropolone < aminotropone << aminothiotropone approximate to amino troponimine. The two last possess the highest kinetic stability compar ed to all known zwitterionic spiro-complexes.