Thiiranes from thiocarbonyl compounds

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]. 

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... 

Heimgartner and co-workers treated a-diazoketones and a-diazoamides 64 with thiones, with and without a catalyst such as Rh(OAc)2 present (1998HCA285). The products were substituted thiiranes 65 and/or substituted 1,3-oxathioles. In all cases, a thiocarbonyl ylide intermediate, which could undergo either a 1,3- or a 1,5-electro-cyclization, was held responsible. The ylide could arise either from addition of a carbene or a carbenoid to S of the thiocarbonyl compound or by loss of N2 from a primary cycloadduct between the diazo and the thiocarbonyl compounds. In one case, such a primary adduct was isolated. The thiirane carboxamides could be desulfurized with (Me2N)3P in tetrahydrofuran (THF) at 60 °C to afford acrylamides 66 (Scheme 11). 

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. 

Difluorocarbene generated from HFPO (1) adds to thiocarbonyl compounds to give thiiranes, as illustrated in the section on oxiranes with the formation of thiirane 30. Tetrafluorothiirane (87) has been made in 30 0% yield from thiocarbonyl fluoride (86) by this method. ... 

When thiocarbonyl and ot-diazocarbonyl compounds are combined, acyl-substituted thiocarbonyl ylides 158 are generated from a nonisolable 3-acyl-1,2,4-thiadiazoline 157 (Scheme 8.36). In addition to giving acylthiiranes 159 and 1,3-dithiolanes 160, dipoles 158 can also 1,5-cyclize to produce 1,3-oxathioles 161. Acyl-thiocarbonyl ylides derived from diazoketones [e.g., HC(0)C(N2)R, R = Ph, f-Bu (219,220) 2-diazocyclohexanone (221)] produce 1,3-oxathioles [e.g., 162 (220), Scheme 8.36], while those derived from diazoesters (218,222,223) lead to thiiranes by 1,3-cyclization. Ylides derived from a-diazocarboxamides form 1,3-oxathioles (e.g., 163) and thiiranes (e.g., 159, R = f-Bu, R = NMePh, R = R" = Ph), depending on the nature of the substituents (220). A related 1,5-cyclization of an aminomethyl-thiocarbonyl ylide formed from dimethyl 3-anilino-2-diazobutanedioate was also reported (224). 

Several fused-ring thiiranes have been synthesized and characterized by H, NMR, and MS. For instances, thiiranes 23-25 are products from the reaction of dimethoxycarbene with 2,2,4,4-tetramethyl-3-thioxocyclobutanone <2002CEJ2184>. Compound 24 was also identified as a product from the cycloaddition of a thiocarbonyl ylide <2001HCA1805>. 

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