Aldehydes from dithianes

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... 

The anions derived from dithianes react with alkyl halides to give the corresponding alkylated dithianes. Their treatment with HgCl2-HgO regenerates aldehydes or ketones, respectively, as depicted below. 

Pi- and Tetrahydrothiophens. - Condensation of mercaptoacet-aldehyde (from 2,5-dihydroxy-1,4-dithiane) with prenal, using potassium carbonate in benzene, gave (236) in 44% yield. Oxidation of (236) with active 2 gave (237), and by addition of Grignard... 

Mercuric oxide/boron fluoride Aldehydes from 1,3-dithianes... 

Write equations for syntheses of ketones and aldehydes from alcohols, alkenes, alkynes, carboxylic acids, nitriles, acid chlorides, dithianes, and aromatic compounds. 

Another useful application of this reaction stems from the fact that dithianes can be desulfiirated with Raney nickel (14-34). Aldehydes can therefore be converted to chain-extended hydrocarbons ... 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Ring enlargement.1 A new route to seven-membered ring systems from a cyclohexenone (1) involves a photocycloaddition of ethylene to provide the bicy-clooctanone 2. Addition of lithio-1,3-dithiane to 2 provides the adduct 3, which on reaction with HgO and HBF4 forms an unstable rearranged hydroxy aldehyde... 

New reaction conditions for the odorless transacetalization providing 1,3-dithianes from aldehydes or ketones, as depicted in Scheme 108 (Section 8.11.10.1), have been published <2006S3801, 2007SC993>. 

The stoichiometric equivalents of halofluorides have been recently applied to transform alkylene dithioacetals into gcm-difluorides.70-71 Dithioacetals such as 1,3-dithiolanes and 1,3-dithianes arc readily obtained from the corresponding carbonyl compounds by the reaction with ethane-1,2-dithiol or propane-1,3-dithiol in the presence of the complexes boron trifluoride-bis(acetic acid) or boron trifluoride-diethyl ether. Using a two-step procedure, a range of aldehydes and ketones can be converted into gem-difluorides under mild conditions. 

The orf/to-formylation of 2-aminopyridines can be effected via the rearrangement of the azasulfonium salt prepared from a 2-aminopyridine, 1,3-dithiane, f-butyl hypochlorite and sodium methoxide (74CC685). The crude sulfilimine (815) was refluxed in f-butanol containing potassium f-butoxide to yield the dithioacetal (816). Hydrolysis of (816) with mercury(II) oxide/boron trifluoride etherate gave the aldehyde (817 Scheme 191). This method should be applicable to the formylation of other heterocyclic amines. 

The syntheses of dithioacetals are generally straightforward [43]. Standard methods may be unselective for multifunctional molecules. Therefore, new procedures have been developed. It has thus been reported that 1,3-dithianes are readily synthesized by reaction of aldehydes, ketones or acetals with 2-stanna-l,3-dithianes under catalysis of organotin triflates [45]. These odourless reagents are prepared from dialkyldichlorotin and 1,3-propanedithiol. 

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