Preparation of thiiranes

Route b involves the formation of one carbon-carbon bond and one carbon-sulfur bond. It belongs to the category of sulfene chemistry143. Sulfene intermediates react readily with diazoalkanes to produce, after the loss of nitrogen, thiirane dioxides. So far, this appears to be the method of choice for the preparation of thiirane dioxides of all types. 

To date, several well-established methods are available for the convenient preparation of thiirane oxides, the two main ones being the controlled oxidation of thiiranes63a and the reaction of sulfenes with diazoalkanes636. 

Historically, the first reactions involving thiocarbonyl ylides involve the preparation of thiiranes and 1,3-dithiolanes from diazomethane and thiocarbonyl compounds reported early in the last century by Staudinger and co-workers (12,13). Similar reactions have been smdied by Schonberg and co-workers (14—16) during the 1960s, but neither was the reaction mechanism understood nor have thiocarbonyl ylides been recognized as key intermediates. [For some remarks to this subject see (8) and (10) in (17).]... 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

Catalyst-mediated decomposition of diazo compounds in the presence of C=S compounds has found application for the preparation of thiiranes in homogeneous systems (68,110,111). Recently, a convenient procedure for the preparation of geminal dichlorothiiranes from nonenolizable thioketones and chloroform under Makosza conditions was reported (112). Another approach to 2,2-dihalogenated thiiranes (e.g., 2,2-difluoro derivatives) involves the thermolysis of Seyferth reagents in the presence of thioketones (113,114a). Nucleophilic dimethoxycarbene was shown to add smoothly to adamantanethione to provide a unique approach to a thiiranone (5, 5 )-dimethylacetal (114b). 

The formal addition of carbenoids to the thiocarbonyl -bond [C + C=S] represents another major route used for the preparation of thiiranes. The reaction of thiocarbonyl compounds with diazoalkenes generally gives good yields of thiiranes (Scheme 11). The mechanism may involve an addition of a carbene across the thiocarbonyl group, especially in the presence of Rh(II) acetate, CuCl, CuS04, or other metal catalysts, but involvement of a zwitterion is also possible . 

Stereoselective preparation of thiiranes from methyl trifluorodithioacetate can be easily achieved at low temperature or room temperature with diphenyidiazomethane, ethyl diazoacetate or a diazo ketone. Depending on the structure of the diazo compound, various amounts of side products, resulting from 1,3-dipolar intermediates, arc obtained. ... 

Scheme 2.8 shows a facile preparation of thiiranes. Desilylation with cesium... 

A new method for the preparation of thiirans from alkenes employs suc-cinimide- or phthalimide-N-sulphenyl chlorides to form addition compounds, e.g. (320 n = 1, 2, or 4), which, on treatment with LiAlH4 at -78 °C, give the corresponding cycloalkene sulphides (58—97%).The method has also been successfully applied to the preparation of thiirans from styrene, methylene-cyclohexane, and norbornene. 

The preparation of thiirans by the reaction of diazo-compounds with thiocar-bonyls has received widespread use. In particular, a number of preparations of... 

Thiirans.—j8-Hydroxyethyl sulphides give low yields of thiirans when heated with triphenylphosphine. A useful method for the preparation of thiirans is to heat j8-hydroxyethyl sulphenyl chlorides with phosphinesthis mild method is remarkable since olefins are not formed by desulphurization. Hence, treatment of the disulphide (102) with chlorine at 25 °C, followed by treatment with triphenylphosphine gave (103), (60% yield), obtained previously in only 13% yield. The proposed mechanism for the formation of these compounds is shown in Scheme 39. The sequence has been applied to a cephalosporin derivative (Scheme 40) inversion... 

Formation.— The methods of synthesis of thiirans have been reviewed. A brief discussion of the preparation of thiirans is part of a review on the reactions of alkali-metal sulphides with organic halides and toluene-p-sulphonates. ... 

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