Thioketenes cycloaddition

Apparently, the reaction involves cycloaddition of nitronate at the C=S double bond of thioketene. This approach can be useful for deoxygenation of labile nitronates. 

As mentioned above (303) (Scheme 3.90, Eq. 1), bis-trifluoromethyl thioketene has the deoxygenating ability toward alkyl nitronates, which is also based on cycloaddition to the C=S bond. 

Cycloaddition may be varied by the use of fluorinated thioketenes in place of ketenes. Olefins and Schiff bases serve as the other component. Thus thioketene 56 cycloadds to a SchifT base to give product 57 in a 79% yield. In a further variation, reaction of dithiobenzoate esters with diphenylketene yields 61% of product 58. ... 

The desUylation strategy has been used for the cycloaddition of the parent thiocarbonyl yhde la with aldehydes and reactive ketones. The product obtained using A-methyl-3-oxoindolinone as the trapping agent corresponds to the spiro-cyclic compound 125 (168). Thioketene (5)-methylide (127) was reported to react with aromatic aldehydes and some ketones to furnish 2-methylene-substituted 1,3-oxathiolanes (128) (51) (Scheme 5.42). 

Thermal and photochemical cycloaddition reactions of 27r-electron species represent an important synthetic approach to four-membered rings. The reactions summarized in this section include 2 + 2 cycloaddition reactions of thioketones, thioketenes, isothiocyanates, sulfenes and iminosulfenes with alkenes, allenes, ketenes, ketenimines and alkynes. 

Thioketene dimers crack at high temperatures into monomers, which then undergo [2 + 2] cycloadditions (Scheme 27) (70JOC3470). 

Cycloaddition of 2-ethoxy-2,3-dihydro-4//-1,3-benzoxazin-4-one with conjugated diene 167 gave tetrahydropyrido[2,l-b][l,3]oxazin-6-ones (168) (71JHC865). Diels-Alder reactions of 3,4-dihydroisoquinolines and thioketenes (169), formed in situ, yielded 4,6,7,116-tetrahydro[l,3]ox-azino[2,3-a]isoquinoline-4-thiones [83AG(E)55 88CB1165],... 

The thermal formation of a nitrene has been invoked to account for the result in the reaction between a sterically hindered thioketene and benzyl azide437 (equation 123). Although initially a 1,3-dipolar cycloaddition between the C=S bond and the azide was expected, the temperature of the reaction (138 °C) led to decomposition of benzyl azide into benzyl nitrene and the subsequent [2 + 1] cycloaddition. 

Cycloaddition with thioketenes 3-Substituted imidazole 1-oxides 228 react with thioketenes to give a mixture of l,3-dihydro-2H-imidazol-... 

We have reported the first electroactivity of a thioketene dimer compound [116]. The CV measurement of 2,4-dibenzylidene-l,3-dithietane (31), which was prepared by a basic dimerization of phenylthioketene derived from ben-zyltriphenylphosphonium chloride, showed irreversible two-step oxidation peaks at 0.25 and 0.61 V vs Ag/Ag+, indicating that 31 acts as a stronger electron donor than 2,6-bisphenyl-l,4-dithiafulvene (30) and TTF (2). The dimer (31) can form a 1 1 CT complex with TCNQ in DMSO. Cycloaddition polymerization of bisthioketene derived from p-xylenebis(triphenylphosphoni-um chloride) gave a -conjugated polymer (32) with thioketene dimer unit in the main chain (Scheme 12). This polymer was the first polymer contain-... 

It has been shown that thioketenes, isothiocyanates, and carbon disulfide can react with hydrazoic acid to form 5-alkyl-, 5-amino-, and 5-thiosubstituted-l,2,3,4-thiatriazoles <1996CHEC-II(4)691>. Most probably these reactions proceed via [3+2] cycloaddition of azide anion to C=S bond. 

It is known that aryl azides undergo 1,3-dipolar cycloaddition reaction with bis(trifluoromethyl)thioketene 156 to form the yellow A3-l,2,3,4-thiatriazolines 159 in very low to fair yield supporting the mechanism of reaction of this thioketene with hydrazoic acid (Equation 14) <1978JOC2500>. 

Cycloaddition reactions of thioketene and isocyanic acid forming four-membered ring products have been studied by means of the ab initio RHF/6-31G method. The two alternative reactions are concerted but nonsynchronous, taking place through twisted or planar four-membered cyclic transition states. The activation barriers were calculated to be... 

Raasch has reported that the thermolysis of a ketenedithioacetal resulted in the dissociation into the corresponding thioketene and thioketone56. It should be noted that it is not the retro[2+2]cycloaddition similar to the carbon analogue, but the cleavage of the germanium-carbon double bond that has taken place in the thermolysis of germene 53. 

Other thermal 1,3-dipolar cycloadditions are the reactions between nitrile sulfides and electron-deficient aldehydes and ketones forming 1,3,4-oxathiazolines (98 Scheme 19) between aryl thioketones and thiofluorenone 5-tosylimide to yield the 1,3,4-dithiazolidines (204) and between thioketene S-oxides and imines, yielding in one case the 1,2,4-oxathiazolidine (136). 

Its structure as determined by an X-ray investigation is shown in Fig 21. It may be understood as a dimer of the assumed phosphathio-ketene intermediate. The cycloaddition of the phosphathioketene corresponds to the behavior of unsubstituted carbaketenes (146) and so is different from that of the phosphaketenes described earlier, while thioketenes dimerize to 1,3-dithietanes (147,148). An asymmetric retro ring cleavage can be initiated if l-thia-3-phosphetane is irradiated by a mercury lamp generating carbon disulfide and the 1,3-diphosphaallene [Eq. (78)] (117, p. 33). 

Bis-(trifluoromethyl)thioketene undergoes cycloaddition to alkenes to give 2-methylenethietanes. ... 

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