Synthesis of Rings with One Sulfur Atom

The formal addition of a carbene to a C=S bond provides one possible route to the thiirane ring. An example is found in the synthesis of methylene-thiirane 411 by reaction of di-fert-butylthioketene with dimethyl diazomalo-nate in the presence of Rh2(OAc)4 (89TL1249). The interaction proceeds via an unstable thioketene 5-methylide 412, which undergoes 1,5-cyclization to the corresponding oxathiole at 50°C (Section VII,B,4), and at higher temperatures undergoes 1,3-cyclization to thiirane 411 (66%). 

The thietane ring contraction with bicyclic ylide intermediacy is the basis of the synthesis of thiiradialene 413 by vacuum pyrolysis of tosylhydra-zone lithium salt 414 (81TL4815). 

Cyclization of diazo sulfides 415 offers a route to stable four-membered cyclic ylides thus, for example, compound 416 (R = Et) was isolated in 53% yield. However, attempts to cyclize sulfide with a phenyl substituent have been unsuccessful (87TL371). 

In five-membered cyclic diazo ketones containing a bivalent sulfur atom, intramolecular ylide formation with subsequent ring contraction becomes 

Thietanone 423 is obtained by desulfurization of cyclic disulfide 424 under the action of bis(methoxycarbonyl)carbene or dkphenylcarbene, generated from the corresponding diazo compounds (85TL5187). This transformation takes place only with disulfides containing bulky substituents. Otherwise, carbene insertion into the S—S bond proceeds with ring expansion (Section VII,C,1). 

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