Thiirene oxides synthesis

The situation is even more problematic in the unsaturated series the elusive thiirenes cannot serve as starting materials for the synthesis of thiirene oxides 18 via direct oxidation, and the laborious synthetic method used to prepare the most commonly known and studied aryl-substituted thiirene oxides 18 does not make the latter attractive as starting materials for preparing the corresponding thiirene dioxides . Fortunately there are much better and versatile methods available for the synthesis of the sulfones 19 (equation 35). 

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). 

Most thiirene dioxides (and oxides) have been prepared through a modified Ramberg-Backlund reaction as the last crucial cyclization step, as illustrated in equation 40 for the benzylic series . Synthesis of thiirene dioxides requires two major modifications of the originally employed reaction first, the inorganic base has to be replaced by the less basic and less nucleophilic triethylamine - and second, the aqueous media has to be substituted by an aprotic organic solvent (e.g. methylene chloride). Under these mild reaction conditions the isolation of aryl-substituted thiirene dioxides (and oxides) is feasible . In fact, this is the most convenient way for the preparation of the aryl-disubstituted three-membered ring sulfones and sulfoxides. ... 

Oxathietes contain all spz hybridized ring carbons and therefore are considered fully conjugated. Unfortunately, no 1,2-oxathietes have been reported to have been isolated in the last decade. This presumably reflects the fact that their open-chain isomers are thermodynamically more stable. Indeed, in a recent publication on the synthesis and stability of thiirene 1-oxides, it was found that heating of sulfoxide 29 in toluene resulted in an excellent yield of the a-oxothioketone 31 (Scheme 3) <2002HAC424>. The isomeric 1,2-oxathiete 30 was postulated to be a transient intermediate but could not be detected. 

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. 

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... 

Formation.—Experimental details are now available for the synthesis of diphenylthiiren 1,1-dioxide (32) from a,a -dibromodibenzyl sulphone by treatment with triethylamine. It is also formed by base-catalysed dehydrohalogenation of a,a-dichlorobenzyl benzyl sulphone, whilst similar treatment of a,a -dibromobenzyl sulphoxide (18) afforded diphenylthiiren 1-oxide. Alkyl-substituted thiiren 1,1-dioxides (33), (34), and (35), which could not be synthesized by this method, were obtained by dehydro-bromination of the appropriate bromothiiran 1,1-dioxides (36), (37), and (38), catalysed by triethylamine or l,5-diazabicyclo[4,3,0]non-5-ene. The bromothiiran 1,1-dioxides were synthesized from the appropriate... 

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