Thiirane oxides synthesis

The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

Methylene thiirane is obtained by thermolysis of several spirothiirane derivatives which are formally Diels-Alder adducts of methylenethiirane and cyclopentadiene or anthracene <78JA7436). They were prepared via lithio-2-(methylthio)-l,3-oxazolines (c/. Scheme 121). A novel synthesis of the allene episulfide derivatives, 2-isopropylidene-3,3- dimethylthiirane (good yield) or its 5-oxide (poor yield), involves irradiation of 2,2,3,3-tetramethyl-cyclopropanethione or its 5-oxide (81AG293). Substituents on the thiirane ring may be modified to give new thiiranes (Section 5.06.3.9). The synthesis of thiirane 1-oxides and thiirane 1,1-dioxides by oxidation is discussed in Section 5.06.3.3.8 and the synthesis of 5-alkylthiiranium salts by alkylation of thiiranes is discussed in Section 5.06.3.3.4. Thiirene 1-oxides and 1,1-dioxides may be obtained by dehydrohalogenation of 2-halothiirane 1-oxides and 1,1-dioxides (Section 5.06.4.1.2). 

Analogous chemistry has been reported with a-chlorosulfoxides, though much less studied. Initial y-dehydrochlorination yields thiirane S-oxides, but from these intermediates two alternative pathways can occur leading to sulfenales and/oi alkenes. The method was shown to be efficient for the synthesis of tetrasubstituted alkenes [417]. 

The synthesis and chemistry of thiirane-1-oxides (episulfoxides) was reviewed in 1997 by Abu-Yousef and Harpp <1997SR1>. One of the many interesting processes discussed there is the thermolysis of thiirane-l-oxide 122, at temperatures exceeding 100 °C, to generate sulfur monoxide. The latter is very reactive and can be trapped by cycloaddition to 1,3-dienes such as 2,3-dimethyl-l,3-butadiene 123 (Scheme 21). 

Thiiranes are very useful starting materials for synthesis of 1-mono- and 1,1-disubstituted taurines <200582122, 2006S315>. Reaction of thiiranes 220 with silver nitrate and ammonia in methanol at room temperature for 30 min gave 221. After reaction of 221 with hydrogen sulfide for 6h to form 222, oxidation of the latter with performic acid gave the corresponding mono- or disubstituted taurines 223 (Scheme 58). 

There are three main synthetic methods for synthesis of thiiranes C-S bond-forming reactions, C-G bond-forming reactions, and two bond-forming reactions. These methods are described in detail in CHEC(1984) and CHEC-11(1996), and the references until 1995 are cited therein <1984CHEC(7)131, 1996CHEC-11(1)174>. Described here are methods published after 1996 for synthesis of thiirane, thiirane-Toxide, thirane-1,1-dioxide, and thiirene-1-oxide. 

There are three main approaches for the synthesis of thiiranes the first is C—S bond formation (Scheme 64), the second is C—C bond formation (Scheme 65), and the third is based on the formation of two bonds (Scheme 66), which includes the reaction of elemental sulfur with alkenes and the reaction of thiocarbonyl compounds or elemental sulfur with carbenes derived from diazo compounds. These methods are described in detail in CHEC-I, and references until 1983 are cited therein <84CHEC-i(7)i7i>. A survey of reports, published mainly after 1983, of the formation of thiiranes, thiirane 5-oxide, and thiirane S,S-dioxides is given in the following sections. 

A unique approach to the synthesis of fused-ring thiiranes and thiirenes involves the utilization of cycloaddition methodology. The use of diphenylthiirene oxide and the corresponding dioxide as dieneophiles in [2 + 2], [4 + 2], and 1,3-dipolar cycloadditions is well established. Often the initial... 

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