CONFORMATIONAL FEATURES AND CHEMICAL BEHAVIOR OF 5H,7H-DIBENZO[B,G][1,5]DITHIOCIN OXIDES - 1,5-OXYGEN SHIFT VIA A DITHIODICATION INTERMEDIATE

Some SH,7H-dibenzo[b,g] [1,5]dithiocin oxides (4-8) and their related compounds 9-13 were prepared and the assignment of the most favorable conformation was carried out on the basis of the characteristic H-1 NM R spectral data. Only a single conformer (BC: boat-chair form) exists for 4, 5, and 8-13, while two conformers (BC and TB: twist-boat form) are apparent for 6 and 7. Oxidation and methylation of 4 gave exclusiv ely a single geometrical isomer (8 and 13, respectively). These result s are interpreted as a sterically preferential attack of electrophiles on the BC conformer of the starting material. A 1,5-oxygen shift of 4 occurred smoothly to give 6 in the presence of trifluoroacetic acid i n CDCl3 solution. The mechanistic investigation is described briefly. Differences in chemical behavior between dibenzodithiocin 12-oxide 4 a nd dibenzothiazocine 12-oxide 2 are also discussed on the basis of the conformational features.