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The title compound 1 was prepared by condensation of 3,5-dibromo- o -phenylenediamine 10 with cyclohexanone and oxidation of the resulting 4,6-dibromo-1,3-dihydro-2 H -benzimidazole-2-spirocyclohexane 5 with manganese dioxide. With sodium 2,3-dichlorophenoxide, sodium benzenesulfinate, or piperidine it reacts by loss of bromine, to give the 6-substituted derivatives 2 , 3 , and 4 , respectively. Morpholine, however, gives 5,7-dibromo-4-morpholino-2 H -benzimidazole-2-spirocyclohexane 15 whilst pyrid-2(1 H )-thione and pyrimidin-2(1 H )-thione give 4-bromo-1,3-dihydro-6-(pyridin-2-ylthio)-2 H -benzimidazole-2-spirocyclohexane 6 and 5,7-dibromo-1,3-dihydro-4-(pyrimidin-2-ylthio)-2 H -benzimidazole-2-spirocyclohexane 14 , respectively. In the presence of 1 or 2 mol equiv. of sodium methoxide an aryne mechanism appears to operate, leading to the formation of either a mixture of 5-bromo-6-methoxy- 11 and 6-bromo-4-methoxy-2 H -benzimidazole-2-spirocyclohexane 12 or 5,6-dimethoxy-2 H -benzimidazole-2-spirocyclohexane 13 , respectively. Oxidation of the title compound 1 with m -chloroperoxybenzoic acid yields the 1-oxide 7 exclusively, which reacts with piperidine and morpholine by loss of the 4-bromine atom, to give compounds 16 and 17 , respectively, in the latter case with concomitant loss of oxygen. |
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