Thiocarbonyl 5-imides 4+2 cycloaddition reactions

Using a similar approach, through [2+3] dipolar cycloaddition reactions, the syntheses of 532 and 533 were accomplished from thiocarbonyl y-imides 531 and norbornene-3,4-dicarboxylate or /ra r-cycloctene <2000T4231>. 

Thiocarbonyl S-imides are excellent dipols in [3+2] cycloaddition reactions. Also [2+4] cycloaddition reactions of thiocarbonyl -imides are known. 

Other reactive olefins, such as enamines and vinyl ethers also participate as dipolarophiles in their reaction with thiocarbonyl 5-imides. Even fulvenes undergo [3+2] cycloaddition reactions. 

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... 

Numerous examples involving the preparation of tetrahydrothiophenes via [3 + 2] cycloaddition of thiocarbonyl ylides with electron-poor alkenes have been reported. Thiobenzophenone (5)-methylide (16), generated from 2,5-dihydro-1,3,4-thiadiazole (15) and analogous compounds, react with maleic anhydride, N-substituted maleic imide, maleates, fumarates, and fumaronitrile at —45°C (28,91,93,98,128,129). Similar reactions with adamantanethione (5)-methylide (52) and 2,2,4,4-tetramethyl-3-thioxocyclobutanone (5)-methylide (69) occur at ca. +45°C and, generally, the products of type 70 were obtained in high yield (36,94,97,130) (Scheme 5.25). Reaction with ( )- and (Z)-configured dipolaro-philes stereospecifically afford trans and cis configured adducts. 

Organic Azides. The 1,3-dipolar cycloadditions of 1 with organic azides require elevated temperatures. T)q)ical products of the reactions of thioketones are W substituted imines, which are formed after decomposition of the initially formed 1,2,3,4-thiatriazole derivates. However, in the case of 1 and aryl azides, the intermediate thiocarbonyl 5-imides (28) intercept 1 to give dispiro-l,4,2-dithiazoles (29) (eq 13).22... 

Thiocarbonyl S-Imides. In eq 13, the interception of a thiocarbonyl S-imide generated in situ from 1 and organic azides is outlined. Similarly, thiocarbonyl 5-imide (30, eq 14) undergoes a 1,3-dipolar cycloaddition with 1 in competition with the formation of the unstable thiaziridine 31, and the corresponding 2,5-dispiro-l,4,2-dithiazolidine (43) and imine 32 are obtained (eq 18). A similar reaction with methyl dithiobenzoate, in which along with 1,2,4-trithiolane (34) a 1,4,2-dithiazolidine of type 43 is formed, is also reported. ... 

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). ° ... 

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