Aldehyde diacetates, formation with

Secondary aliphatic amines reacted readily with mercaptoaldimines (279), which could be prepared readily by the action of Na/NH3 on the aldehyde diacetals (278). The resulting N,N- dialkyl derivatives (280) were alkylated on sulfur by a-halocarbonyl compounds such as bromoacetic acid the resulting products (281) underwent spontaneous ring closure and aromatization via loss of the secondary amine to yield the acids (282 Scheme 97). Decarboxylation of the acids (282) furnished the substituted thieno[2,3-6 ]thiophenes (283). The use of other a-halocarbonyl compounds, such as bromoacetone or phenacyl bromide for the alkylation, led to the formation of the 2-acetyl or 2-benzoyl derivatives, (284) and (285) respectively (76AHC(19)123). 

The moisture- and air-stable ionic liquids, l-butyl-3-methylimidazolium tetra-lluoroborate [bmim]BF and l-butyl-3-methylimidazolium hexafluorophosphate [bmim]PFg, were used as green recyclable alternatives to volatile organic solvents for the ethylenediaimnonium diacetate-catalyzed Knoevenagel condensation between aldehydes or ketones with active methylene compounds. As described by Su et al. [57], the ionic hquids containing a catalyst were recycled several times without decrease in yields and reaction rates. In the case of 2-hydroxybenzaldehyde, the reactions led to the formation of 3-substituted coumarin derivatives in high yields of up to 95% (Scheme 17.11). When ethyl cyanoacetate was used, 2-imino-27f-l-benzopyran-3-carboxyhc acid ethyl ester was formed. 

The formation of 1,1-diacetates 5 from aldehydes 4 and Ac20 dates back to early systematic studies by Knoevenagel [9]. A representative example is given with the preparation of compound 5a in Scheme 8.1. Several groups have since then developed improved protocols for acylal formation [10]. It was realized that these gem-diacetates such as compound 5b are perfect substrates for palladium-catalyzed... 

A mixture of epoxides 483 obtained on oxidation of 482 with dimethyldioxirane, when exposed to ferric chloride provided, as the kinetically controlled product, the a-aldehyde 484, which without purification was reduced to the a-alcohol 485. The exclusive formation of 484 is believed to occur via the benzyl cation 486, generated by Lewis-acid opening of the oxirane ring, suffering a stereospecific kinetic 1,2-hydride shift The amino alcohol 487 obtained after sequential removal of O-benzyl and N-tosyl groups from 485, on treatment with triphenylphosphine and iodine in the presence of imidazole furnished the tetracyclic base 488, which was oxidised to the ketone 489. Trapping of the kinetically generated enolate of 489 as the silylether, followed by palladium diacetate oxidation yielded the enone 490. The derived... 

In the BASF process the 1,2-diacetate is the substrate for the hydroformylation step. It can be prepared either directly via oxidative acetoxylation of butadiene using a selenium catalyst or via PtCl4-catalyzed isomerization of the 1,4-diacetate (see above). The latter reaction affords the 1,2-diacetate in 95% yield. The hydroformylation step is carried out with a rhodium catalyst without phosphine ligands since the branched aldehyde is the desired product (phosphine ligands promote the formation of linear aldehydes). Relatively high pressures and temperatures are used and the desired branched aldehyde predominates. The product mixture is then treated with sodium acetate in acetic acid to effect selective elimination of acetic acid from the branched aldehyde, giving the desired C5 aldehyde. 

The fact that ketones, aldehydes and geminal diacetates are readily available from these reactions illustrates their complementarity to reactions with allylsilanes. Specifically, the equivalency of allylic ethers to homoenolates allows for the formation of compounds extended... 

The diacetate 84 underwent deacetylation followed by acetal formation to afford 85. Selective opening of the cyclic acetal ring followed by Collins oxidation afforded the aldehyde intermediate 86. Treatment of 86 with allylsilane derivative 87 afforded a mixture of diastereoisomeric alcohols 88 in a 1.7 1 ratio. The major product 88 was oxidized to the corresponding ketone 89, which upon removal of the protecting groups led to the formation of (-)-sesbanimide A (2). 

Reactions of Carboxylic Acids and their Derivatives.—A novel series of /8-lactones has been obtained from 17,20-dihydroxypregnan-21-oic acids (406) and (407). The reaction occurs, along with formation of the 17,20-diacetate, in acetic anhydride-pyridine. Lactonization is most efficient with the 20a-isomer (406) which affords the less-hindered rrans-20-acetoxy-lactone (408). The crystalline lactones (408) and (409) are stable at - 20 °C but suffer slow decarboxylation at room temperature or in refluxing benzene to give the trans- (410) and cis-enol acetate (411), respectively, of the 17-aldehyde (412). In a similar way the dihydroxy-acids (406) and (407) react with ethyl chlorocarbonate-pyridine to give 20-cathyl-21, 17a-lactones several novel transformations of these products are described. 

The oxidation of a ( )-flavanone with Tl(ni) nitrate, Pb tetracetate, phenyliodonium diacetate (PIDA), or [hydroxyl(tosyloxy)iodo]benzene in trimethyl orthofonnate affords the corresponding ( )-2,3-dihydrobenzo[h]furan derivative as a major product. The structures, including the relative stereochemistry, and a plausible mechanism of formation are reported. The preferred formation of a flavone from the ( )-flavanone by PIDA is explained by quantum-chemical calculations on the intermediate formed by the addition of this reagent to the enol ether derivative of the ( )-flavanone." Formation of mixed anhydrides by rapid oxidation of aldehydes, activated by pivalic acid, Bu OCl in presence of pyridine and MeCN is catalysed by TEMPO (2,2,6,6-tetramethylpiperidin-l-oxyl). The anhydrides can be converted in situ to esters, secondary, tertiary or Weinreb amides in high yield. Oxidation of the aldehyde to 2-propyl esters is also possible using only catalytic amounts of pivalic acid." ... 

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