Thiacycle

While enantioselective transition metal catalysis continues to be important, several useful all-organic catalysts have been developed over the past few years. Tomislav Rovis of Colorado Stale University has reported (J. Am. Chem. Soc. 2004, /26, 8876) that the triazolium salt 5 catalyzes the enantioselective Stetter-type cyclization of 4 to 6. The cyclization also works well for the enantioselective construction of azacyclic, thiacyclic and carbocyclic rings. 

Coordination polymerisation of heterocyclic monomers comprises polymerisation and copolymerisation processes of such monomers as oxacyclic monomers, especially epoxides [2,61-71], thiacyclic monomers like episulphides [72-76], azacyclic monomers [77,78] and phosphacyclic monomers [79]. Monomers with an exocyclic oxygen atom, such as cyclic esters like lactones [80-90] and lactide [90-92], cyclic acid anhydrides [93-98], cyclic carbonates [99,100] and related monomers, belong to oxacyclic monomers undergoing coordination polymerisation or copolymerisation. 

Although thiacyclic monomers do not play such an important role in coordination polymerisation as oxacyclic monomers, some polymerisation of tiiranes with coordination catalysts deserves attention, especially considering the polymerisation stereochemistry ... 

Note that some general considerations of ring-opening polymerisation originate from studies of the coordination polymerisation of tiiranes. Other thiacyclic monomers that contain an endocyclic sulphur atom and an exocyclic oxygen atom, such as monothiocarbonates, are instead analogous to five-membered cyclic carbonates. 

Schmid has successfully transformed the five-membered ring sulfonium salt (192) into the 17-mem-bered ring sulfur thiacycle (197) in four iterations (Scheme 17). The products (194), (193) and ( )-(194) are form in a ratio of 67 27 6. The presence of tetrahydrothiophene (193) is the result of ylide formation at the more-substituted allylic site of salt (192) followed by [2,3] sigmatropic rearrangement. The... 

IH)-2-Benzothiopyrans. l,2-Bis(benzylthio)acetylenes undergo cyclization to give the novel thiacyclic compounds. 

Thiacycles. involves lithiation an transfer to conjugated in the presence of c CpjTiSj, CpjZrS,). ... 

Thiacycles. An expedient preparation of 1,3-dithiol-2-thiones from 1-alkynes involves lithiation and consecutive treatment with sulfur and carbon disulfide. For sulfur transfer to conjugated dienes, such as dithiin formation, the yields are significantly enhanced in the presence of catalytic amounts of metallocene polysulfides (Cp MoS, CpjWS, Cp2TiS5, Cp ZrSj). ... 

Recent progress in the synthesis of oxepanes and medium ring ethers. Tetrahedron, 68, 6999-7018. (d) Vilotijevic, L, Jamison, T. F. (2009). Epoxide-opening cascades in the synthesis of polycyclic polyether natural products. Angewaudte Cheruie lutematioual Edition, 48, 5250-5281. (e) Snyder, N. L., Haines, H. M., Peczuh, M. W. (2006). Recent developments in the synthesis of oxepines. Tetrahedron, 62, 9301-9320. (f) For medium-ring thiacycles Rosowsky, A. 1972. In Weissberger, A., Taylor, E. C. (Eds.) Heterocyclic Compounds. Wiley, New York. Vol. 26. 

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