1,3-DISELENETANES AND 1,3-DITHIETANES DERIVED FROM CAMPHOR - FORMATION, STRUCTURE, STEREOCHEMISTRY, AND OXIDATION TO SELENOXIDE AND SULFOXIDE PRODUCTS

The reaction of camphor enolate with elemental selenium, followed by aerial oxidation, afforded chiefly the endo,endo-dicamphoryl diselenide 3 and 4 selenide. However, in the presence of methyl iodide, the principal products were the syn- and anti-1,3-diselenetanes 5 and 6, formed by the dimerization of the putative selenoketone intermediate 12. The products 5 and 6 were also obtained by the base-catalyzed elimination of HCN from the camphoryl selenocyanate 14, followed by dimerization of the same intermediate 12. The reaction of camphor enolate with sulfur and methyl iodide did not produce the corresponding 1,3-dithietanes, but mainly a mixture of dicamphoryl sulfide and camphoryl methyl sulfide stereoisomers 15-18. Base-catalyzed elimination of camphoryl thiocyanate 19 afforded the anti-1,3-dithietane 21 as the sole stereoisomer via thioketone 20. Oxidation of 21 with PhICl(2) produced a single sulfoxide isomer 24. Further oxidation of the latter with m-CPBA gave a mixture of bis-sulfoxides 25 and 26 and trioxide 27, while exhaustive oxidation of 21 gave the bis-sulfone 29. Treatment of the syn-1,3-diselenetane 5 with PhICl(2) resulted in oxidation of the endo and exo selenium atoms to afford selenoxides 30 and 31 in the ratio of 91:9, respectively. Similar oxidation of the anti isomer 6 produced the selenoxide 32 and a smaller amount of 30 by ring opening and reclosure. X-ray crystal structures of the anti-1,3-diselenetane and -dithietane 6 and 21 were determined.