Thioketenes reactivity

Ketenes and related compounds have been reviewed extensively (1 9). For the synthesis and synthetic uses of conjugated ketenes see Reference 10. Ketenes with three or more cumulated double bonds have been prepared (11,12). The best known is carbon suboxide [504-64-3] 3 2 preparative uses and has been reviewed (13—16). Thioketenes (17,18), ketenimines (19—21), and their dimers show interesting reactivity, but they have not achieved iadustrial importance to date. 

Thiirenes have been isolated in argon matrices at 8 K by photolysis of 1,2,3-thiadiazoles or vinylene trithiocarbonates (Scheme 151) (80PAC1623, 8UA486). They are highly reactive and decompose to thioketenes and alkynes (Scheme 22). Electron withdrawing substituents stabilize thiirenes somewhat, but no known thiirene is stable at room temperature unlike the relatively stable thiirene 1-oxides and thiirene 1,1-dioxides. 

The enolates of other carbonyl compounds can be used in mixed aldol reactions. Extensive use has been made of the enolates of esters, thiol esters, amides, and imides, including several that serve as chiral auxiliaries. The methods for formation of these enolates are similar to those for ketones. Lithium, boron, titanium, and tin derivatives have all been widely used. The silyl ethers of ester enolates, which are called silyl ketene acetals, show reactivity that is analogous to silyl enol ethers and are covalent equivalents of ester enolates. The silyl thioketene acetal derivatives of thiol esters are also useful. The reactions of these enolate equivalents are discussed in Section 2.1.4. 

This and similar catalysts are effective with silyl ketene acetals and silyl thioketene acetals.155 One of the examples is the tridentate pyridine-BOX-type catalyst 18. The reactivity of this catalyst has been explored using a- and (3-oxy substituted aldehydes.154 a-Benzyloxyacetaldehyde was highly enantioselective and the a-trimethylsilyoxy derivative was weakly so (56% e.e.). Nonchelating aldehydes such as benzaldehyde and 3-phenylpropanal gave racemic product. 3-Benzyloxypropanal also gave racemic product, indicating that the (i-oxy aldehydes do not chelate with this catalyst. 

Thioketenes (83) are generally unstable and very reactive, although bis (trifluoromethyl)thioketene (83 R1 = CF3) is stable enough for isolation. 

In many cases, the product is toxic as in the case of the conjugate of trichloroethylene, which is thought to be responsible for the aplastic anemia induced in calves fed trichloroethylene-extracted soybean oil meal (27). The unstable product shown in brackets (Fig. 7.20) has the potential to lose HC1 to form a reactive thioketene or tautomerize to form the reactive chlorothioacetyl chloride (27). 

Dekant W, Urban G, Gorsman C, et al. 1991. Thioketene formation from y-haloalkenyl 2-nitrophenyl disulfides models for biological reactive intermediates of cytotoxic S-conjugates. J Am Chem See 113 5120-5122. 

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). 

The reactive thiol/thioketene produced by the (3-lyase is an alkylating fragment, which binds to protein, DNA, and GSH. The fact that one of the locations of C-S lyase is in mitochondria may explain why this organelle seems to be damaged. Damage to the respiratory chain will lead to depletion and a shortage of ATP, which is vitally necessary for the activity of the kidney in terms of active uptake and secretion. 

In sharp contrast to the thioketenes, carbon disulfide S=C=S, carbon oxysulfide 0=C=S and the isothiocyanates R-N=C=S are stable compounds although highly reactive, and are widely used in organosulfur chemistry. Some of their reactions with organometallics have been mentioned previously (see Section 2.8.3). 

Photodissociation of thiophene yields several products among them thioketene, CH2=C=S, produced by C,C cleavage317. More synthetic utility possesses the thiocyanohydrins which, by vacuum-gas phase dehydrocyanation, yield the corresponding reactive thioaldehydes318 (equation 53). These thiocyanohydrins can be mono- and... 

A kinetic study of the Ph2BOH-catalysed reactions of several aldehydes with 2 revealed that the rate of the disappearance of 2 followed first-order kinetics and was independent from the reactivity of the aldehydes used. Taking into account this result, we have proposed the reaction mechanism in which a silyl enol ether is transformed to the corresponding diphenylboryl enolate before the aldol addition step takes place (Scheme 13.1). The high diastereoselectivity is consistent with the mechanism, in which the aldol step proceeds via a chair-like six-membered transition state. The opposite diastereoselectivity in the reaction with the geometrical isomers of the thioketene silyl acetal shown in Table 13.3 also supports the mechanism via the boron enolate, because this trend was also observed in the classical boron enolate-mediated reactions in dry organic solvents. Although we have not yet observed the boron enolates directly under the reaction conditions, this mechanism can explain all of the experimental data obtained and is considered as the most reasonable one. As far as we know, this is the first example of... 

Addition of phenylethynethiolate or -selenate to the carbene complex 185 (M = Cr or W, R = Me or Et, E = S or Se) affords an anionic adduct (186) which, unexpectedly, contains a reactive thioketene function. Electrophiles can attack either at the sulfur or at the carbon a thereto to produce coordinated carbenes or thio- and seleno aldehydes and esters [H4J45). 

New methods have been developed for the generation of the reactive thiocarbonyl ylid (255) and the thioketene JS-methylides (256), both of which depend on the fragmentation, by loss of... 

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