Sulfur-containing carbenes

Sulfur-containing carbenes are known and review articles have been pubhshed. - The diazo precursors are prepared either by the action of weak bases on the appropriate N-nitrosocompound or by the use of diazo transfer reactions.. izs The sulfonylcarbene 241 undergoes an addition reaction to olefins and acetylenes (Scheme 46) to give 242 and 243, respectively. 

The chemistry of the polynuclear-ring, sulfur-containing carbene thioxathen-ylidene-S,S-dioxide 244 indicates easy cycloaddition to styrenes.It reacts fi"om its singlet state and behaves as an electrophilic carbene (Scheme 47). 

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

From the results with the isolable ylides 350, it can be concluded that the fate of less stable, non-isolated sulfonium ylides depends dramatically on their respective substituents 336,338). Thus, the outcome of these reactions is programmed at the ylide stage and not during interaction of a presumed metal carbene with the sulfur-containing substrate. 

Schollkopf and co-workers have synthesized a number of cyclopropanone acetals by the addition of various sulfur- and oxygen-containing carbenes to ketene diethylacetals (Table 3).26>27> Similarly, cyclopropanone dithioacetals may be prepared by the addition of the Ws-thiomethyl and Ws-thiobenzylcarbenes 12a, b to olefins.29) However, cyclopropanone acetal formation by this method requires double bonds with considerable electron enrichment and the yields are generally low. With unsubstituted olefins such as cyclohexene, the carbenes 12 a, b tend to form dimeric and trimeric products such as 13 and 14, instead of the double bond addition products. 

Rees, C. W., Smithen, C. E., The Reactions of Heterocyclic Compounds with Carbenes, 3,57. Reid, S. T., The Photochemistry of Heterocycles, 11,1 The Photochemistry of Oxygen- and Sulfur-Containing Heterocycles, 33, 1 Photochemistry of Nitrogert-Containing Heterocycles, 30, 239. 

Carbene cyclization reactions offer a convenient and efficient method for the synthesis of five-membered sulfur-containing rings. These may involve both carbene insertion into a C—H bond and ylide formation. 

Free carbene 429 generated by photolysis or thermolysis of the diazo compound cyclizes into the sulfonium ylide, which undergoes a thia-Stevens rearrangement to 430 in 19% yield. The same result was obtained using the corresponding p-tosylhydrazone sodium salt as a carbene precursor (83JA6096). Rh(II)-catalyzed decomposition of sulfur-containing diazo... 

An unusual system where the carbene carbon is part of a six-membered ring, but with two adjacent nitrogens, has been the subject of a short series of papers.Reactions of hypervalent sulfur-containing precursors with a platinum(O) complex take place under mild conditions, yielding new complexes 145 and 146 (Scheme 36). Little detail is given, but it is believed the displaced sulfur ends up as Ph3P=S. 

In addition to the miscellany of dihalocarbenes, the principal successes have been in the formation of sulfur containing (Sect. 4.6) and unsaturated carbenes (Sect. 4.7). 

The reaction of an osmium carbene cluster containing the cyclic carbene ligand = C(CH=CH)2C(Ph)H which is side on bound to a nonacarbo-nyltriosmium unit with either elemental sulfur/NEt3 or cyclohexene sulfide also afforded a rf-thioketone complex.184... 

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