1.3- oxathiolanes, 1,3-dithiolanes

Recently, Sc(OTf)3 has been widely used in many protection reactions such as methoxymethylation [69], tetrahydropyranylation [70], O-glycosidation [71], acylation [72, 73], esterification of alcohols [74], and thioglycosidation of glycols [75]. Scandium salts such as Sc(OTf)3 and SCCI3 were also found to be efficient and recyclable catalysts for conversion of carbonyl compounds to 1,3-oxathiolanes, 1,3-dithiolanes, and 1,3-dithianes [76, 77]. By employing this protocol, chemose-lective oxathioactalization of aldehydes in the presence of ketones was achieved (Scheme 12.34) [78]. 

For 1,3-dithiolanes the ring is flexible and only small energy differences are observed between the diastereoisomeric 2,4-dialkyl derivatives. The 1,3-oxathiolane ring is less mobile and pseudoaxial 2- or 5-alkyl groups possess conformational energy differences (cf. 113 114) see also the discussion of conformational behavior in Section 4.01.4.3. 

Dithiolanes are not affected by these conditions, but a 1,3-oxathiolane is cleaved (100% yield). 

O2, hv, hexane, Ph2CO, 2-5 h, 60-80% yield. 1,3-Oxathiolanes and dithiolanes are also cleaved by these conditions. 

The section on the cleavage of 1,3-dithianes and 1,3-dithiolanes (pp. 203-205), should be consulted since many of the methods described there are also applicable to the cleavage of oxathiolanes. 

Cyclohexane-1,2-dione reacts with ethylene glycol (TsOH, benzene, 6 h) to form the diprotected compound. Monoprotected 1,3-oxathiolanes and 1,3-dithiolanes are isolated on reaction under similar conditions with 2-mercaptoethanol and eth-anedithiol, respectively. ... 

Substituted A,A-dialkyl(cycloalkyl)furfurylamines and their quaternary salts, 2-substituted 1,3-dioxolanes, oxathiolanes, and -dithiolanes, as antagnoists and muscarinic receptors 98F1. 

The reaction with sulfides occurs efficiently only when the resulting carbon-centered radicals are further stabilized by a a-heteroatom. Indeed, (TMSfsSiH can induce the efficient radical chain monoreduction of 1,3-dithiolane, 1,3-dithiane, 1,3-oxathiolane, 1,3-oxathiolanone, and 1,3-thiazolidine derivatives. Three examples are outlined in Reaction (12). The reaction of benzothiazole sulfenamide with (TMS)3SiH, initiated by the decomposition of AIBN at 76 °C, is an efficient chain process producing the corresponding dialkylamine quantitatively. However, the mechanism of this chain reaction is complex as it is also an example of a degenerate-branched chain process. 

Dihydro-1,4-oxathiins (336 Z = 0) and 5,6-dihydro-1,4-dithiins (336 Z = S) are easily obtained from 1,3-oxathiolanes (335 Z = 0) and 1,3-dithiolanes (335 Z=S), respectively, by treatment with bromine (9IS223), A-bromosuccinimide (94T7265), chlorine (87JOC5374, 91S223), or sulfuryl chloride (88JCR(M)1401>. 

Perio, B., Dozias, M.-J. and Hamelin, J., Ecoffiendly fast batch synthesis of dioxolanes, dithiolanes, and oxathiolanes without solvent under microwave irradiation, Org. Process. Res. Dev., 1998,2, 428. 

Pyrolytic methods involve the use of dithiolane S, S -dioxides as starting materials which, upon heating, afford reactive thioaldehydes, such as trifluorothioacetaldehyde, trapped as the Diels-Alder adduct369,370 (equation 82). In equation 80 an enethiolate was formed, and this feature has been employed also in the cleavage of the oxathiolane 78. The silver vinylthiolate 79 thus obtained was applied in the preparation of new antibacterial cephem derivatives371. 

Rhodium-catalysed decomposition of methyl diazoacetate (1.2 equiv.) in the presence of 1,3-dithiolane yields mainly dithiane (31) as a mixture of diastereoisomers.34 Ring-expanded product (32) and ring-opened products (33) arising from a second condensation of the carbene are also isolated, albeit in low yield. Similar reactivity is observed with 1,3-oxathiolane. 

Scheme 5 Scale-up synthesis of dioxolanes, oxathiolanes, and dithiolanes...

Lewis acids readily isomerize both 1,3-dioxolanes and 1,3-oxathiolanes in ether solution. The reaction proceeds by coordination with the oxygen atom in the latter case since 1,3-dithiolanes do not isomerize under the same conditions. With trityl carbonium ion, an oxidative cleavage reaction takes place as shown in Scheme 6. Hydride extraction from the 4-position of 2,2-disubstituted 1,3-dioxolanes leads to an a-ketol in a preparatively useful reaction. 1,3-Oxathiolanes are reported to undergo similar cleavage but no mention of products other than regeneration of the ketone has been made (71CC861). Cationic polymerization of 1,3-dioxolane has been initiated by a wide variety of proton acids, Lewis acids and complex catalytic systems. The exact mechanism of the polymerization is still the subject of controversy, as is the structure of the polymer itself. It is unclear if polymerization... 

In what is effectively a desulfurization reaction, 1,2-dithiolane 1,1-dioxide reacts exothermically with aminophosphines such as tris(diethylamino)phosphine in benzene solution to give 1,2-oxathiolane 1-oxide in excellent yield (71JOC322). The reaction, which requires a slight excess of the aminophosphine, is shown in Scheme 41. 

The palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a [42] and aziridine 20b [39] with the activated olefin 4a for the formation of five membered cyclic ether 21a and pyrrolidine derivative 21b has also been reported in our laboratories. The mechanistic issue is very much similar to that discussed in Scheme 9. Pd(0) catalyst added oxidatively to 20 to produce the 7r-allylpalladium complex 22. The Michael addition of a hetero nucleophile in 22 to the activated olefin 4a gives 23 which undergoes intramolecular nucleophilic attack on the inner 7r-allylic carbon atom to give the cy-clized products 21 and Pd(0) species is generated (Scheme 10). Similarly, the palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a with the N-losylimincs 24 is also known (Scheme 11) [43]. Intermolecular cycloaddition of vinyl epoxides and aziridines with the heterocumulenes such as isocyanates, carbodiimides and isothiocyanates is also known [44,45]. Alper et al. reported the regio- and enatioselective formation of the thiaolidine, oxathiolane, and dithiolane derivatives by the palladium-catalyzed cyclization reaction of 2-vinylthiirane with heterocumulenes [46]. 

Dithiolanes and 1,3-oxathiolanes also undergo carbene insertion on treatment with methyl diazoacetate in the presence of Rh2(OAc)4, to give 1,4-dithiane-2-carboxylates and... 

---