Bicyclic Vinyl Sulfides by Ring Expansions of Spirocyclic Dithioketal Systems

Article abstract of DOI:10.1021/jo00222a008

Our objective was to prepare sulfur-containing bicyclo<10.6.0>- and -<10.5.0>alkenes for future photochemical studies.Prototypes having a seven-membered heterocyclic ring with two sulfurs were obtained by one-atom ring expansion of a spirocyclic 1,3-dithiane 1-oxide (11b).A similar sequence applied to the homologous 1,3-dithiepine 1-oxide (17) enlarged it to its corresponding eight-membered heterocycle (18).A two-atom-ring growth of a β-hydroxy-1,3-dithiane promoted by P2O5 was developed with a monocyclic model compound (23a).The product (24) is a1,5-dithiacyclooctene with one sulfur vinylic and the other allylic.When the scheme was applied to the appropriate spirocyclic 1,3-dithiane system (29a), P2O5 produced the corresponding 12/8 bicyclic alkene (31a) with a tetrasubstituted ?-bond.With POCl3/Py, the 6 -> 8 rearrangement afforded the trisubstituted olefin (30a), which separately could be isomerized to alkene 31a.The action of P2O5 on a spirocyclic β-hydroxy-1,3-dithiolane (29c) gave the desired 12/7 ring system as a binary mixture of olefins (30b, 31b), which converted entirely to the more stable tetrasubstituted isomer when treated with HCl gas.One-atom (6 -> 7) ring expansion in α-hydroxy-1,3-dithianes was tested on a monocyclic analogue (32a) and its acetate ester (32b).Hot POCl3/Py successfully enlarged the alcohol to an alkene having a 1,4-dithiepane skeleton (36).Pyrolysis of the acetate (32b) effected the same ring expansion.