Thioaldehyde

Nonchelation control also results from the trifluoroborane-mediated addition of the following silylketcne acetal to 2-thioaldehydes. The diastereomeric ratios of the adducts surpasses 98 2... 

Selenoaldehydes 104, like thioaldehydes, have also been generated in situ from acetals and then directly trapped with dienes, thus offering a useful one-pot procedure for preparing cyclic seleno-compounds [103,104], The construction of a carbon-selenium double bond was achieved by reacting acetal derivatives with dimethylaluminum selenide (Equation 2.30). Cycloadditions of seleno aldehydes occur even at 0 °C. In these reactions, however, the carbon-selenium bond formed by the nucleophilic attack of the electronegative selenium atom in 105 to the aluminum-coordinated acetal carbon, may require a high reaction temperature [103], The cycloaddition with cyclopentadiene preferentially gave the kinetically favorable endo isomer. 

Vallee Y., Ripoll J. L. Synthesis of Thioaldehydes, Thioketones and Thioketenes... 

The addition of H2S to an aldehyde or ketone can result in a variety of products. The most usual product is the trithiane (8). ° ot-Hydroxy thiols (5) can be prepared from polychloro and polyfluoro aldehydes and ketones.Apparently, compounds 5 are stable only when prepared from these compounds, and not even for all of them. Thioketones (6) can be prepared from certain ketones, such as diaryl ketones, by treatment with H2S and an acid catalyst, usually HCl. They are often unstable and tend to trimerize (to 8) or to react with air. Thioaldehydes are even less stable and simple ones apparently have never been isolated, though t-BuCHS has been... 

Heteroatom Diels-Alder reaction of thioketones and thioaldehydes... 

Hetero Diels-Alder reactions of 114 with thioaldehydes and thioketones were also reported to give the syn addition products exclusively [64]. 

Reaction of aliphatic aldehydes with H2S and TCS 14 at room temperature in the presence of pyridine leads to the adducts 596, which can be converted by NaH in DMF, via the adducts 597 and the intermediate thioaldehydes 598, into their sodium salts 599. These sodium salts 599 can be trapped by alkyl- or aUyl hahdes in up to 91% yield to give the vinyl sulfides 600 [147] (Scheme 5.47). 

Free intermediate thioaldehydes 598 or 602 and the selenoaldehydes 605 and HMDSO 7 are obtained in THF at 0°C on treatment of aliphatic and aromatic aldehydes with bis(trimethylsilyl)thiane 601 or bis(trimethylsilyl)selenide 604 in the presence of traces of butyllithium, while trapping the sensitive intermediate thio- or selenoaldehydes 602 and 605 with cyclopentadiene or cyclohexadiene to furnish mixtures of endo and exo Diels-Alder adducts such as 603 a and 606 a and 603 b and 603 b [148-150], the exo/endo ratio of which can be controlled [150] (Scheme 5.48). Analogous reaction of ketones such as 2-adamantanone or acetylene ketones with MesSiXSiMes 608 (a. X=S (601) b. X=Se (604)) in the presence of... 

On transforming the cyclopentenone 1431 into the trimethylsilyloxy diene 1432 the ensuing Diels-Alder cyclization gives rise to 69% tricychc compound 1433 [10] (Scheme 9.8). For Diels-Alder-reactions of thioaldehydes, selenoaldehydes, or unsaturated nitroso compounds with cyclopentadiene, see the reactions of 602 to 603 and of 605 to 606 in Scheme 5.48 and of 1092 to 1093 in Scheme 7.43. For Diels-Alder-reactions of silyloxyazadienes such as 510 with maleic anhydride to give 511, see Scheme 5.29. 

In a quite different approach, the 1,3-oxathianes 79 undergo a tandem [4++2 ] -eye 1 oaddi ti on -elimination with alkenes yielding 3,4-dihydrothiopyrans a preference for the tis-isomer was noted (Scheme 55), The oxathianes, which are readily synthesised, thus serve as a,P-unsaturated thioaldehydes <00TL371>. 

Aldehydes can be converted into thioaldehydes by a similar reaction with bis(trimethylsilyl) sulfide catalyzed by BuLi (equation II). This disilyl sulfide has been used indirectly for conversion of aldehydes into thioaldehydes via boron trisulfide (11, 63). 

The reaction of thioaldehydes, generated from phosphonium ylides and sulphur with secondary amines such as dimethylamine, leads to thioamides. If the thioaldehydes possess a a-hydrogen atom enamines are produced (equation 103)326. 

Concomitant C-Si cleavage by tetra-n-butylammonium fluoride and extrusion of a phenylthiolate anion from ot-trialkylsilyldisulphides provides a route to reactive thioaldehydes [44],... 

TBA-F in THF (0.01 M, 200 ml) is added slowly with stirring over 30-60 min to the a-silyldisulphide RCH(SiR3)SSAr (5 mmol). The mixture is stirred until all of the disulphide is consumed and the reactive thioaldehyde is reacted in situ without isolation. 

The SH bond is sufficiently weaker than the CH bonds so that the RS radical would be the dominant species formed. At high temperatures, it is likely that the RS decay leads to the thioaldehyde... 

The disappearance of the thioaldehyde at these temperatures would closely resemble that of the aldehydes namely,... 

The radical formed in reaction (8.144) then decomposes to form an alkyl radical and a thioaldehyde molecule that is,... 

Density functional and semiempirical AMI molecular orbital calculations have been used to investigate substituent effects on site selectivity in heterocumulene-hetero-diene4 + 2-cycloadditions between ketene imines and acroleins.The new and novel heterocumulenes a, /3-unsaturated thioaldehyde S -oxides (97) behave as both diene... 

---