Thermolysis of O-allyl S-alkyl dithiocarbonates of codeine and isocodeine.

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Abstract
The reactions of O-allyl S-alkyl dithiocarbonates of codeine and isocodeine were examined under thermal and catalytic conditions. Heating of a xylene solution of xanthates (3, 4, and 5) gave the corresponding S-allyl S-alkyl dithiocarbonates (6, 7, and 8) via [3,3] sigmatropic rearrangement in high yields, overcoming the difficulty of attack on the hindered .alpha.-face. On the other hand, in the case of isocodeine, the formation of xanthates followed by the rearrangement took place without heating to afford the dithiocarbonates (9, 10, and 11). Furthermore, compound 10 rearranged with extrusion of COS to give the sulfide (14). The reactions of 3, 6, and 9 with phospholine-palladium (0) complex and a Lewis acid as catalysts were also examined. When 3 or 6 was treated with (Ph3P)4Pd, elimination reaction proceeded to give 6-demethoxythebaine (17). The reactions of 6 and 9 with TiCl4 yielded the corresponding cyclic dithiocarbonates 18 and 19.

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