Thioketene S-oxides

In an interesting contrast to the photochemical behavior of the simpler sulfine system, the photolysis of thioketene S-oxides such as 25 in carbon tetrachloride leads to the corresponding thioketenes in excellent yield36. This photochemical deoxygenation is... 

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). 

The oxidation of thioketene (245) by nitrones (246) of the 1-pyrroline 1-oxide type furnishes a-thiolactones (thiiranones) (247) (Equation (40)) <77AG(E)722>. But the oxidation of thioketene S-oxide gives thioketone S-oxide via thiiranone S-oxide (Scheme 87). 

Reactions of 3-dimethylamino-2H-azirines (248) with thioketene S-oxides (249) provide the thiiranimine derivatives (250) (Scheme 90 and Table 40) <82AG(E)694>. 

Diazomethane reacts in a 1,3-dipolar fashion across the C=C of thioketene S -oxides to give good yields of the 1 1 adducts (145). In contrast, thioketenes are known to react across the C=S bond. 

Thiiranimines are hetero-analogues of methylenecyclopropanes, and have been little studied. It has been demonstrated that dimethylamino-azirines (210) react with thioketene S-oxides with remarkable ease, probably by 1,3-dipolar cycloaddition. The initially formed adduct (211) collapses to the thiiran (212) yields are very good, and the products appear to be relatively thermally stable and not easily desulphurized. 

Thioketen tert.-Butyl-isopropyl- -S-oxid Ell, 942 (S-Oxigenier.)... 

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). ° ... 

In contrast, thioketene 5-oxides react with azomethines via a [3-1-2] cycloaddition in which the C=S=0 group participates as a 1,3-dipol to give SO". ... 

Oxidation of thioketenes with peracids affords thioketene 5 -oxides (R2C=C=S=0) , a class of heterocumulenes also treated in this chapter. A review of thioketene -oxides was published in 1985. Also, alkylidenethioketenes (R2C=C=C=S) and thiocarbonyl-5 -sulfides (R2C=S=S) are known. The higher homologue, CH2=C=C=C=S, is generated by irradiation of matrix isolated 2,5-diiodothiophene. ... 

A -1,3,4-Thiadiazoline-1 -oxides (146) (Equation (18)) are formed by addition of diazo compounds (R2C=N2) to sulfines (R R C =S=0). The adducts from diazomethane and aryl substituted sulfines are unstable and give the thiadiazole (147) via a Pummerer-type aromatization <84CHEC-I(4)545>. The A -thiadiazoline-1,1-dioxide (149) has been produced by oxidation of the hydrazone (148) (Equation (19)) and treatment with sulfur dioxide <84CHEC-i(4)545>. 2-Alkylidenethiadiazolines can be obtained from the dipolar addition of diazo compounds to thioketenes <83CB66, 90TL3571, 92HCA1825>. 

The synthesis of the C29-C43 EF segment 479 is summarized in Scheme 68. Methylation of 467 under Prater s conditions stereoselectively afforded 2,3-anti compound 468 (dr = 5-8 1). After TES protection followed by thioester reduction, aldol reaction of the resulting aldehyde with thioketene acetal afforded a-alcohol 469 under Felkin-Anh selectivity. TES deprotection and silver-mediated lactonization followed by TES protection and lactone reduction gave lactol 470. Dehydration, debenzylation, and oxidation furnished aldehyde 471, which was transformed to benzotriazolyl amide 472. 

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