Thiiranes, cycloadditions

Both (17) (74TL2841) and (18) (76JA4325) undergo cycloadditions at the double bond without disruption of the thiirane ring (80JOC2962, 80JA6633). This type of reaction has been used to convert (17) to the Dewar pyrrole (20) via the tricyclic thiirane (19) (77JA7350). 

Alkylidene sulfenes (75), generally prepared by the dehydrohalogenation of alkylsulfonyl chlorides, add readily to electron-rich multiple bonds. For example, with enamines, the thietane dioxide (e.g., 76) is formed diazoalkanes yield thiirane dioxides (episulfones) and imines (Schiff bases) afford 1,2-thiazetidine 1,1-dioxides. There are available numerous reviews of sulfenes, including cycloaddition reactions.102... 

When thiocarbonyl derivatives are treated with an excess of electrophilic carbene complex, alkenes are usually obtained [1333-1336], The reaction is believed to proceed by the mechanism sketched in Figure 4.18, closely related to the thiocarbonyl olefination reaction developed by Eschenmoser [1337], Few examples have been reported in which stable thiiranes could be isolated [1338], The intermediate thiocarbonyl ylides can also undergo reactions similar to those of carhonyl ylides, e.g. 1,3-dipolar cycloadditions or 1,3-oxathiole formation [1338], Illustrative examples of these reactions are given in Table 4.22. 

When planning reactions of thiocarbonyl compounds with electrophilic carbene complexes it should be taken into aceount that thiocarbonyl compounds can undergo uncatalyzed 1,3-dipolar cycloaddition with acceptor-substituted diazomethanes to yield 1,3,4-thiadiazoles. These can either be stable or eliminate nitrogen to yield thiiranes or other products similar to those resulting from thiocarbonyl ylides [1338]. 

Cheletropic reactions, in which a single atom is added or extruded, comprise a special case of cycloaddition reactions. Figure 14.4 displays correlation diagrams for two typical cheletropic reactions, the loss of SO2 from a thiirane dioxide (Figure 14.4a) and the loss of CO from a norbornadienone (Figure 14.4b). The addition of a carbene to an olefin is another example which is discussed below (Figure 14.9a). 

The thiirane donates sulfur to the thioketone, thus furnishing olefin and thiobenzophenone 5-sulfide (122) which can be intercepted in 1,3-dipolar cycloadditions to activated acetylenes or thiones455. 

Extrusion (or elimination) of sulfur from thiiranes and thiirenes is a facile process. Virtually all thiiranes and thiirenes, as well as their V-oxides and V,V-dioxides, undergo thermal extrusion of the sulfur moiety with increasing facility according to the trend S << SO < S02. Sulfur monoxide produced in this way can be utilized in cycloaddition processes, for example, from 2 in refluxing toluene with 2,3-dimethyl-l,3-butadiene in a chelotropic addition <1997JOC8366>. 

Another domino process which is initiated by a 1,3-dipolar cycloaddition, and which allows the synthesis of either (3-lactams or thiiranes, was recently reinvesti-... 

Some examples of the preparation of oxirancs, thiiranes and aziridines by the reaction of diazo compounds with trifluoromethyl-substituted carbonyl and thiocarbonyl compounds. imines,and oximes arc known. However, as noted in Section 2.1.1.6.2.5.1., carbenes are not always the reactive species. Thus, the reaction can consist of a 1,3-dipolar cycloaddition, followed by decomposition of the resulting pyrazolinc. 

Methyl 2-diazo-.3 3,3-trifluoropropanoate (11) and thiobenzophenone (12) undergo cycloaddition at 50 C to yield a single product, namely the thiirane 13. ... 

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