Thioaldehydes and Thioketones

Thioaldehydes and Thioketones. (i) Synthesis of simple aliphatic thioalde-hydes and thioketones by reductive cleavage reactions of unsaturated sulphides. (ii) Photochemistry of thioketones. (iii) Synthesis of 

---

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

Heteroatomic dipolarophiles are competent in the dipolar cycloaddition of nitronates. The in situ generated thioaldehydes and thioketones react with sUyl nitronate 120 to afford the 1,4,2-oxathiazolidine in good yield (Table 2.36) (113-116). 

It is very well known that polymers of high commercial value are obtained from formaldehyde by addition polymerization of its carbon-oxygen double bond. Not so well known is the addition polymerization capability of the carbon-sulfur double bond, probably because none of the polymers so obtained has yet become commercially acceptable. However, the polymerization chemistry of the carbon-sulfur double bond has been the subject of a number of studies and these have defined the preparation and properties of polythioformaldehyde, polythio-acetone, polymers from a small number of higher thioketones, and polymers from fluorine analogs of thioaldehydes and thioketones. The monomers have great reactivity beyond polymerization, and their general chemistry has been discussed in earlier reviews (/, 2). 

Usually these heteroaldehydes and heteroketones are generated in solution in the presence of suitable substrates and immediately trapped. The synthesis, properties, and reactivity of thioaldehydes and thioketones have been the subject of several reviews.1-5 The chemistry of selenocarbonyl compounds has likewise been reviewed in recent years.6-9... 

Another route to thioaldehyde and thioketone complexes uses the tungstate [W(CO)5SH] as the precursor. When [W(CO)5SH] was treated with ketones in the presence of trifluoroacetic acid, thioketone complexes [W(CO)5 S = C(R1)R2 ] were formed. Analogously, thiobenzaldehyde complexes were obtained from [W(CO)sSH]- and benzaldehydes bearing electron-releasing para substituents. Benzaldehyde, benzaldehydes with electron-withdrawing substituents, and aliphatic aldehydes did not react. Presumably, the binuclear dianion [p,-S W(CO)5 2]2 is an intermediate in the reaction, as on acidification of a mixture of [ju,-S W(CO)5 2]2 and p-N, A -dimethylaminobenzaldehyde the thioaldehyde complex [W(CO)5 S = C(C6H4NMe2-p)H ] is formed.143... 

Full details98 have been published on the use of hexamethyldisilathiane in the generation of thioaldehydes and thioketones, which can be trapped in situ (equation 23). The... 

The corresponding 1,3-dithiolane S -oxides were prepared by oxidation of the thioacetals with m-chloroperbenzoic acid (mCPBA) and, notably, this approach has proven successful in the obtention of both thioaldehydes and thioketones. 

Retro-Diels-Alder reactions giving thiocarbonyl compounds are favored when simultaneously a comparatively stable diene is formed1. This is the case with anthracene and cyclopentadiene Diels-Alder adducts 81 and 82 which, upon heating, afford a wide array of thioaldehydes and thioketones (equation 84). These adducts are stable at room temperature and have become a convenient way of storing very reactive thiocarbonyl compounds. Cyclopentadiene is the cheapest and most reactive diene for use in Diels-Alder reactions. Also, strain in the bridged cycloadducts facilitates retro-Diels-Alder cleavage224. 

The preparation of thioaldehydes and thioketones bearing an adjacent electron-withdrawing group, such as a carbonyl group, has been an intense area of study (Table 3). 

Simple thioaldehydes and thioketones are too unstable to exist and attempts at their preparation lead to appalling smells (Chapter 1). The problem is the poor overlap between the 2sp2 orbital on carbon and the 3sp2 orbital on sulfur as well as the more or less equal electronegativities of the two elements. Stable thiocarbonyl compounds include dithioesters and thioamides where the extra conjugation of the oxygen or nitrogen atom helps to stabilize the weak C-S bond. 

Electrophilic attack on metallathiacycles leading to conjugated thioaldehydes and thioketones... 

Nakayama and co-workers have shown that 3, 4-di-/er/-butylthiophene 1-oxide can serve as trapping agents for unstable thioaldehydes and thioketones. Benzothiophenium salts 118 have been shown to undergo [4+2] cycloaddition with a number of dienes to give compounds of type 119<03JOC731>. 

Thioaldehydes and thioketones are not known in the pure condition. When hydrogen sulphide is passed into an aqueous solution of aldehyde, an oil is formed which appears to be a mixture of thioaldehyde and its polymer (CH3.CHS)3. When acetone is treated in the same way, thioacetone, CH3.CS.-CH3, is probably formed along with other substances. 

General. Several reviews on 2,4-bis(4-methoxyphenyl)-l,3, 2,4-dithiadiphosphetane disulfide, Lawesson s Reagent (LR), have appeared since 1992, which deal with its chemical properties and reactions and, in particular, its use in synthetic chemistry. The most valuable and comprehensive one was authored by Jesberger et al. Li et al. have written a Chinese review article on new applications of LR in organic s)fntheses. A modification of LR which carries tert-butyl substituents (13) has been described by Foreman. Compound 13 is better soluble in organic solvents and thus more reactive than LR. Reports on the use of LR in syntheses of thioaldehydes and thioketones have appeared. 

Hetero Diels-Alder reactions of 3,4-di-fcrf-butyIthiophene 1-oxide with thioaldehydes and thioketones take place exclusively at the syn-jt-face with respect to the S=0 bond, like the Diels-Alder reactions with ketones. Thiophosgene and adamantanethione can also react with 3,4-di-(erf-butylthiophene 1-oxide to afford the corresponding syn-tr-face products (Scheme 44) [49]. 

Scheme 44 5y -it-face-selective Diels-Alder cycloaddition of 3,4-di-fert-butylthiophene 1-oxide with thioaldehydes and thioketones [49]... 

With this reagent, Na3[Fe(CN)5NH3], aromatic nitroso compounds give strongly colored complexes in which the molecule of ammonia is substituted by a molecule of a nitroso compound (36). A positive reaction is also given by hydrazines, thioaldehydes, and thioketones. 

Transcription of these rules for naming thioaldehydes and thioketones causes no problems as will be demonstrated by just two examples. 

Thioaldehydes and thioketones oxidized at sulfur are additively named as thioaldehyde oxides, dioxides and thioketone oxides, dioxides, respectively. Besides, the traditional names sulfine and sulfene are still used for these species. 

---