9- Membered cyclic sulfide

The proton affinities (gas phase) of thiirane and other three-membered heterocycles have been determined azirane (902.5), thiirane (819.2), phosphirane (815.0), oxirane (793.3 kJ moF ) (80JA5151). Increasing s character in the lone electron pairs decreases proton affinities. Data derived from NMR chemical shifts in chloroform indicate the order of decreasing basicity is azirane > oxirane > thiirane (73CR(B)(276)335). The base strengths of four-, five- and six-membered cyclic sulfides are greater than that of thiirane. 

Transannular cyclizations of nine-membered cyclic sulfides provided a novel route to thioanalogues of swainsonine derivatives. Treatment of the enantiopure polyhydroxylated thiacyclononane derivative 48a with trimethylsilyl iodide yielded the bicyclic sulfonium salt 49a as a single diastereomer, as shown in Equation (16) <2003JOC3311 >. The presence of a C2-axis and the complete regio- and stereoselectivity of the transannular substitution led to a single configurationally homogeneous product irrespective of the fact that the sulfur atom would attack C-5 or C-6. 

The 3- and 4-membered cyclic sulfides, referred to as thiiranes (also episulfides) and thie-tanes, respectively, are easily polymerized by both cationic and anionic initiators, such as... 

In thiepanes 89, 90, and 92, transannular attack at C3 or C4 could lead to a mixture of polyhydroxylated tetrahy-drothiopyrans or tetrahydrothiophenes. However, by the reaction of substrates 89 (or 90) and 92 with Me3SiI, 91 and 93 were obtained exclusively (free of any five-membered cyclic sulfides), respectively, through a seven- to six-membered ring-contraction reaction. In both cases, as predicted for an Sn2 transannular cyclization and due to the presence of a -symmetric axis (Scheme 11), only one diastereoisomer was obtained. Episulfonium salt was proposed to be formed by a stereo- and regiospecific process, followed by a ring contraction toward the more stable tetrahydrothiopyran derivative. 

The Shimizu group investigated the potential of another structural type of sulfide organocatalyst, 5- and 6-membered cyclic sulfides [211]. These sulfides were prepared by biocatalytic reduction using baker s yeast. In particular the 5-... 

The enantioselective synthesis of bicyclic sulfonium salts 135, starting from thionane ring system, has been reported <2003JOC3311>. The synthetic strategy is based on a stereo- and regiospecific transannular cyclization of nine-membered cyclic sulfides, mediated by TMSI or carried out under acidic catalysis (Scheme 24, stereochemistry omitted). Each compound was prepared in two enantiomerically pure forms starting from the corresponding (R,R)- and (A, -intermediate. 

A similar treatment as outlined for BCMO (p. 101), a four-membered cyclic ether, has later been applied by Goethals to four-membered cyclic sulfides and cyclic amines. The kp/kj ratios were determined for a series of substituted thietanes and aaetidines monomer structures and determined values of kp/kj are given in the following order ... 

Treatment of thietanes with chloramine T gives N-tosylsulfilimines, for example, 126. Acyclic and five-, six-, and seven-membered cyclic sulfides all react more rapidly than thietane. The mechanism has been investigated. The IR stretching vibrations of the S-N-SO2 system are at 948 and 759 cm", and the nmr spectrum of 3,3-dimethylthietane 1-tosylsulfilimine in benzene and chloroform suggests an equatorial conformation for the sulfilimine. Oxidation of this sulfilimine gives the sulfoximine derivative, 127. The two diastereomeric tosyl-sulfilimines of 3-methyl-3-phenylthietane complex at nitrogen with silver ion. ... 

Heterocycles containing sulfur atoms are usually less strained than the corresponding ethers. Thus, the 5-membered cyclic sulfide-tetrahydrotiophene (THT) does not polymerize in contrast to THF (cf. additional discussion on THF on p. 23). 

This same reaction can also be used to prepare five- and six-membered cyclic sulfides. Treating a 1,4-dihaloalkane with Na2S gives a five-membered cyclic sulfide treating a 1,5-dihaloalkane with NajS gives a six-membered ring. 

In 2008, the Katsuki group reported a highly enantioselective oxidation of cyclic sulfides using the (salalen)Al complex 33 as the catalyst (Scheme 19.41).Oxidations of six-membered cyclic sulfides, thiochroman-4-ones, furnished the corresponding sulfoxides in high yield with excellent enantioselectivities. Five-membered cyclic sulfide and seven-membered cyclic sulfide were also good substrates for the aluminium-catalysed system. In these oxidations, over-oxidation of sulfoxides was observed, and the corresponding sulfones were obtained in 5-20%. 

A s-sulfide accelerates the solvolysis nearly 3000-fold compared to the simple alkyl halide and approximately 15,000-fold compared to the B-chloroether. On the other hand, the y-sulfide offers no assistance apparently closure to the four-membered cyclic sulfon-ium ion cannot compete with direct displacement by the external nucleophile. 

A well-known characteristic of medium-sized rings (8- to 11-membered) is their ability to undergo facile transannular reactions. Cere et al. found that acid-catalyzed transannular cyclizations of 8-10-membered 7,5-unsaturated cyclic sulfides yield fused bicyclic sulfonium salts independently of the geometry of the double bond <1998J(P2)977>. 

The acid-catalysed transannular cyclization of 8-10-membered y,5-unsaturated cyclic sulfides (59) or (60) yields c/x-fused bicyclic sulfonium salts (61) independently of the geometry of the double bond. The rate varies linearly with the acidity function -(Ho h with a slope of 1. The rate variations span a range of about 10 , the maximum rate difference being observed for the ( /Z)-thiacyclooct-4-ene pair. The data are consistent with the classical interpretation of the intramolecular reactivity in terms of internal strain of the substrate and/or of the transition state. ... 

Cyclic sulfides treated with triethyl phosphite eject sulfur and form a new ring less one member [577], From compounds containing sulfur in three-membered rings (thiiranes) alkenes are formed in high yields [291, 294. The same reaction can be achieved with triphenyl phosphine [291]. 

Table 1. The unit cell parameters of cyclic eight-membered selenium sulfides... 

The most effective synthesis for thietanones is the eliminative cyclization of halogenated ketones with hydrogen sulfide ions in the presence of bases (Eq. lOb). The reaction of 1,3-dibromoketone derivatives with sodium hydrogen sulfide produced 3-thietanones in association with a five-membered cyclic disulfide (Eq. 10c). 

New cyclic 4-, 5-, 7-, 8-, and 10-membered carbon sulfides and 5-membered oxidosulfides 93PS(74)295. 

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