Thiocarbonyl 5-sulfides , cycloadditions

The benzotrithioles (127) have been prepared for R = Pr and OMe and the X-ray structure has been determined in the latter case [95CL321]. The hindered 1,2,4-trithiolane (128), a thiocarbonyl sulfide cycloaddition product, has been formed as a byproduct [95HCA1499]. The benzodithiatellurole and benzothiaselenatellurole (129) have been prepared and the former can be further converted into the spiro compound (130) [95TL587]. 

The 1,3-dipolar systems involved in the cycloaddition reaction with cumulenes include azides, nitrile oxides, nitrile imines, nitrones, azomethine imines and diazo compounds. However, some 1,3-dipolar systems are also generated in the reaction of precursors with catalysts. Examples include the reaction of alkylene oxides, alkylene sulfldes and alkylene carbonates with heterocumulenes. Carbon cumulenes also participate as 1,3-dipols in [3+2] cycloaddifion reactions. Examples include thiocarbonyl sulfides, R2C=S=S, and l-aza-2-azoniaallenes. 

Alkylidenethioketenes and thioketene 5-ylides (R2C=C=S=CH2) are also described in this chapter. The latter were trapped by an intramolecular cycloaddition reaction to give dithiolanes. Also, propadieneselon, CH2=C=C=Se, is described in this chapter. The unusual extended system, ArN=C=C=C=S, was recently generated by flash vacuum thermolysis ". Thiocarbonyl- -sulfides are treated as Thiosulfines in Section 4.2.2. 

Another interesting example of a photochemi-cally induced domino process is the combination of the photocyclization of aryl vinyl sulfides with an intramolecular addition as described by Dittami et al. [901 as intermediate a thiocarbonyl ylide can be assumed. The domino-Norrish I-Knoevenagel-allyl-silane cyclization developed by us allows the efficient stereoselective formation of 1,2-trans-subsituted five- and six-membered carbocycles.1911 A photochemical cycloaddition of enamino-aldehydes and enamino-ketones with the intermediate formation of an iminium salt followed by addition to allylsilanes gives access to novel bicyclic heterocy-des. New examples of photochemically induced... 

Nitrogen-containing heteroaromatic compounds react with (chloromethyl)[(tri-methylsilyl)methyl] sulfide in the presence of CsF to afford fused 1,3-thiazolidines of type 130. These compounds are the result of a formal [3 + 2] cycloaddition of the parent thiocarbonyl ylide la across the C=N bond (170). In these cases, the formation of the five-membered cycloadduct is believed to occur in two steps via an intermediate onium ion. 

Numerous structures containing the thiocarbonyl ylide dipole are conceivable. Incorporation of the thiocarbonyl ylide dipole into a bicyclic heterocyclic system is possible by the conversion of the cyclic thione (203) into the ring-fused mesoionic system (204). The thiocarbonyl ylide dipole (205) undergoes cycloaddition with both alkenic and alkynic electron-poor dipolarophiles in refluxing benzene or xylene so that, after extrusion of hydrogen sulfide or sulfur, respectively, from the initial 1 1 cycloadducts (206) and (207), a ring-fused pyridinone is formed. The method has been used for the annelation of pyridinones to the imidazole, 1,2,4-triazole, thiazole and 1,3,4-thiadiazole systems... 

Dithiins 367 have been prepared in moderate yields by [4 + 2] cycloaddition of in situ formed thioenones with thiocarbonyl groups (Scheme 171) <2004SL2159, CHEC-III(8.11.9.2)824>. The thio compounds were generated from trialkylsilyl- or trialkylstannyl-tetrahydropyranyloxy allenes 366 using bis(trimethylsilyl)sulfide (HMDST) and CoC nbE O. 

Reaction with thiocarbonyl compounds. The thiocarbonyl compounds obtained by photochemical oxidation of phenacyl sulfides can be trapped efficiently by a 1,3-dipolar cycloaddition with 1 to give 2. This heterocycle can be cleaved to carbonyl compounds by Bu4N F or (CjH5)3N HF. This process is more efficient and more general than photolysis of phenacyl sulfides in the presence of oxygen. 

Nonphotochemical cycloadditions of hexafluorothioacetone to alkenes (vinyl ethers, vinyl sulfides, " cyclohexene, and dimethyl maleate " ) have been observed, as illustrated for methyl vinyl ether. The formal addition of thiocarbonyl fluoride to tetrafluorethylene to give hexafluorothietane occurs on thermolysis at 600-700° (lO " mm) of a copolymer of the two components. " QO-Dimethyldithiooxalate undergoes a thermal cycloaddition to quadricyclane to give thietane 51a. ... 

Ring-fused mesoionic anhydro triazolium hydroxide systems 131 (84M11) that incorporate the thiocarbonyl ylide dipole undergo cycloaddition with both olefinic and acetylenic dipolarophiles the unstable 1 1 cycloadducts 132 and 133 yield ring-fused a-pyridinones 134 by elimination of hydrogen sulfide or sulfur, respectively (Scheme 42) (79JOC3803). 

If the rearrangement is carried out in the presence of elemental sulfur, diminished yields of benzoxathiocins are obtained under these conditions, formation of thiocarbonyl 5-sulfides (thio-sulfines), which are trapped via intramolecular cycloaddition, accounts for the major products formed (Scheme 36) <92CC600). 

H shift. In some cases, e.g., methyl azidoacetate, the sulfur atom extmded in the course of the reaction is intercepted by 1 to give a thiocarbonyl 5-sulfide (thiosulfine, 33), which subsequently undergoes a 1,3-dipolar cycloaddition with 1 yielding... 

Thiocarbonyl S-SulSdes (ThiosulSnes). The formation of the symmetrical 1,2,4-trithiolane (34, eq 14) is the evidence for the intermediacy of thiosulfine 33 formed by a sulfur transfer from thiaziridine 31 to 1. The mixed 1,2,4-trithiolane (51) (eq 22) can result either from the [2 + 3]-cycloaddition of thiobenzophenone 5-sulfide (53) with 1 or from 33 with thiobenzophenone. Both pathways are conceivable for the formation of 51 in a three-component reaction including 1, thiobenzophenone, and phenyl azide. Tetraphenyl-1,2,4-trithiolane (54) undergoes a [2 + 31-cycloreversion and releases 53, which is trapped by 1 to afford 51 (eq 22). The latter is stable under the reaction conditions. ... 

High-level quantum-chemical calculations on the 3 + 2-cycloadditions of thioformaldehyde 5 -imides, S -methylide, S-oxide, and 5-sulfide have been reviewed. Theoretical studies on the 1,3-dipolar cycloaddition between thioketene 5-oxide and methyleneimine show that this reaction is concerted but non-synchronous. Adamantanethione 5-methylide reacts with thiocarbonyl compounds to produce 1,3-dithiolanes. A density-functional-theory study of the cycloaddition of the sulfine H2CSO predicts the 2 + 3-mechanism having the lowest pathway, with an activation barrier of 12.3kcalmoP. R The thermal and photochemical reactions of fluorenethione 5-oxide (69) with cyclooctyne (70) involves an initial 1,3-dipolar cycloaddition to produce the adduct (71), followed by an efficient sulfur transfer to cyclooctyne to produce the enone (72) and the dithiin (73) (Scheme 26). ° ... 

Adamantanethione was also used as a dipolarophile to trap 26, and the [3+2] cycloadduct is obtained in 81 % yield. Cyclooctyne is also used as a dipolarophile for trapping diphenylthiocarbonyl S-sulfide and p-chlorodiphenylthiocarbonyl 5-sulflde. The [3+2] cycloaddition reaction of the thiocarbonyl 5-sulflde 30 with diarylsulfides... 

The cumulenes discussed in this book are subdivided into carbon- and noncarbon cumulenes, and the 1-carbon cumulenes (sulfines, sulfenes, thiocarbonyl S -imides and thiocar-bonyl S -sulfides) are excellent dipolar species. The 2-carbon or the center-carbon cumulenes (carbon dioxide and carbon sulfides) are less reactive but their imides (isocyanates, isothiocyantes and carbodiimides) readily participate in many of the discussed reactions. The 1,2-dicarbon cumulenes (ketenes, thioketenes and ketenimenes) similarly participate in cycloaddition reactions, as well as the more exotic 1,2-dicarbon cumulenes (1-silaalene, 1-phosphaallene and other metal allenes). In contrast, 1,3-dicarbon cumulenes are only... 

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