Abstract
Several eight-membered heterocyclic organobismuth(III) compounds have been synthesized and their antibacterial activity examined. Bis(2-bromobenzyl) sulfide 1 was dilithiated through halogen-metal exchange with t-BuLi and treated with BiCl3 to give 12-chlorodibenzo[c,f][1,5]thiabismocine 2. This compound was obtained as an inseparable mixture of two stable conformers 2a and 2b, as revealed by 1H-NMR, the latter being predominant. On heating above 80 °C, the former isomerized and 2b formed as the single conformer. By treatment with p-tolyl Grignard reagent 3, compound 2 was converted to 12-(4-methylphenyl)dibenzo[c,f][1,5]thiabismocine 4, the sulfur atom of which was oxidized with MPBCA in preference to the bismuth to yield sulfoxide 5. The eight-membered cyclic bismuth(III) compounds thus obtained were examined for their antibacterial activity using a colon bacillus Escherichia coli (E bacillus) and a micrococcus Staphylococcus albus (St bacillus). The cyclic organobismuth(III) compounds exhibited stronger activity against St bacillus rather than E bacillus, and the eight-membered cyclic compounds worked more than the six-membered ones. The highest antibacterial activity was observed for the ones in which the transannular hypervalent bond was formed between the bismuth and the heteroatom elements.
