Aldehydes dithiane derivatives

DDQ, CH3CN, H2O (9 1), 0.5-6 h, 30-88% yield. Dithiane derivatives of aromatic aldehydes give thioesters in low yields dithiolanes are not effectively cleaved. 

One of the most direct methods of synthesizing acylsilanes involves deprotonation and silylation of the 1,3-dithiane derivative of an aldehyde. Unmasking the carbonyl group reveals the acylsilane (Figure Si6.4). 

The third and final general protocol for the hydrolysis of 5 5-acetals exploits the very easy reaction of the sulfur atom of an S-acetal with alkylating agents such as iodomethane, trimethyl- or triethyl-oxonium tetrafluoroborate, and methyl triHuoromethanesuLfonate to form the corresponding trialkylsulfonium salts. Ley s approach to the potent insect antifeedant Azadirachtin [Scheme 2 81]135,171,172 benefited from an easy S-alkylation-hydrolysis sequence. In a synthesis of Epiantillatoxin, a more difficult liberation of an aldehyde from its dithiane derivative was accomplished without rearrangement of a p,y-alkene into conjugation [Scheme 2,82].173... 

Protection of an enone as the dithiane derivative without destruction of an accompanying dioxane was accomplished during a synthesis of Aphidicolin [Scheme 2.90]181 by using the hw-trimethylsilyl ether of propane- 1,3-dithiol in the presence of zinc iodide as the catalyst.182 In the same vein, a synthesis of a fully functionalised B-ring system of Taxol [Scheme 2.91] included the selective thio ace tali sat ion of an aldehyde in the presence of a ketone using silver(I)-cata-lysed thioacetalisation with EtS-TMS and chlorotrimethylsilane.183... 

Dithiolanes and dithianes derived from ketones are more reactive than the aldehyde-based substrates. For electron-rich aromatic compounds the use of 7V-iodosuccinimide instead of A -bromosuccinimide or 1,3-dibromo-5,5-dimethylhydantoin is recommended to avoid ring bro-mination. 

Dithioacetals of aldehydes are sources of carbanions and hence may be used to form new C-C bonds in reactions in which the formerly electron-deficient character of the aldehydic carbon has been reversed. The 1,3-dithianes derived from formaldehyde or a higher aldehyde may be metallated and then alkylated (Scheme 2.27). Hydrolysis of the dithioac-etal is usually carried out in the presence of a thiophilic (sulfur seeking) metal salt such as a mercury salt. The insoluble sulfides cause the equilibrium to move in favour of the parent carbonyl compound. 

A convenient, electrochemically based procedure for regenerating aldehydes and ketones from their 1,3-dithiane derivatives was developed [137] ... 

Hydrolytic cleavage of the C-O bond of bicyclic, tetracyclic, and steroidal enolates with HF-SbFs induces their isomerization to the corresponding ketones (Scheme 14.41) [104]. Rearrangement of dienones to aromatic compounds is also promoted by HF-SbFs (Scheme 14.42) [105]. Ring expansion of methyl penicilli-nates is achieved by SbCls to give thiazepine derivatives [106]. 1,3-Dithianes derived from ketones and aldehydes are deprotected with SbCls by means of a single-electron-transfer mechanism [107]. 

Heteroatom Oxidation. Oxidation of organosulfur confounds with PhI(OAc)2 is noted in a number of different contexts. A particularly useful method for deprotection of dithiane-derived aldehydes and ketones employs PhI(OAc)2 in aq acetone (eq 65). Related to this process, organosulfides may be selectively oxidized to sulfoxides by employing the supported reagent PhI(0Ac)2/Al203 or with a combination of PhI(OAc)2 and Ac20. ... 

A number of other systems can be utilized as the synthetic equivalent of a nucleophilic carbonyl group, particularly in Sn2 alkylation reactions. Dithiane derivatives of aldehydes can be converted to nucleophiles by lithiation. The resulting anion is easily alkylated. Hydrolysis leads to a ketone. Lithiated vinyl ethers and... 

A dithiane synthesis can convert an aldehyde to a ketone. The aldehyde is first converted to its dithiane derivative, which is deprotonated and alkylated. A mercuric chloride-assisted hydrolysis gives the ketone. Show how this technique might be used to convert benzaldehyde to benzyl phenyl ketone. 

Treatment of 2-lithio-l,3-dithiane derivatives with methyl disulphide yields the orthothioformate 83, which upon hydrolysis in alcoholic solvents furnishes an ester . This method may provide a useful route for the conversion of sensitive aldehydes to esters and carboxylic adds. 

Thiols react with aldehydes and ketones to give dithioacetals or dithioketals. 1,2-Dithiols react with aldehydes and ketones to give 1,3-dithiolane derivatives and 1,3-dithiol reactions to give 1,3-dithiane derivatives. 

Thiols react with aldehydes and ketones to give dithioacetals or dithioketals. 1,2-Dithiols react with aldehydes and ketones to give 1,3-dithiolane derivatives and 1,3-dithiol reactions to give 1,3-dithiane derivatives 34, 35, 36, 37, 38, 77, 78, 79, 80, 81. Primary amines react with aldehydes and ketones to give imi-nes. Secondary amines react with ketones and sometimes with aldehydes to give enamines 39, 40, 41, 42, 43, 44, 45, 46, 47, 61, 73, 84,89, 93. 

Improved conditions, using Zn-EtaAlCl, have been reported for the olefination of aldehydes or ketones with methyl dichloro- or trichloro-acetate leading to a,/3-unsaturated esters or their y-chloro-derivatives, respectively. A full account has been published of the oxidation of dithiane derivatives (161) to esters (162) using Pb(OAc)4, followed by desulphurization overall yields of the esters are 51—58% for this rather peculiar reaction. In contrast, relatively standard methodology can be used to convert esters RCH2C02Et into their unsaturated homologues (163) in four steps and in satisfactory yields throughout. ... 

By comparison with dithian derivatives, bis(phenylthio)alkyl-lithiums have been almost ignored as acyl carbanion equivalents, probably because they are relatively unreactive to alkyl halides. However, they react readily with aldehydes and ketones, and trifluoroacetic acid treatment of the products so formed converts them into the very ketone which would have resulted from simple alkylation-deprotection (Scheme 3), thus providing a synthetically convenient alternative. ... 

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