Cyclic acetals in the synthesis of polyoxamacrocycles

Russian Chemical Bulletin - A selective one-pot procedure to access 8-, 9-, and 10-membered polyoxacycles bearing ester functions was elaborated. The procedure involved the copper-promoted...     

The synthesis of acetylenic acetals

Zinc chloride on silica gel is an active catalyst for the condensation of ethyl orthoformate with terminal acetylenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1172–1173, May, 1990.     

Novel synthesis and application of mixed acetals (acetyl methyl acetals)

A novel synthetic method for mixed acetals (acetyl methyl acetals) by electrolysis of hemithioacetals derived from methoxy- (phenylthio)methane is newly developed. Synthetic application of these mixed acetals as an aldehyde equivalent is also demonstrated.     

A rapid means for the synthesis of aldehyde acetals

Conclusions A convenient rapid method has been proposed for the acetalization of aldehydes by ethyl orthoformate in the presence of trace amounts of perchloric acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 921–923, April, 1986.     

The first synthesis of cyclopropanone acetals from the reaction of Fischer carbene complexes with ketene acetals

The reaction of iso-propoxy stabilized Fischer carbene complexes with ketene acetals gives moderate to excellent yields of cyclopropanone acetals when carried out under a carbon monoxide atmosphere. This is in contrast to the known reaction of methoxy substituted complexes which give cyclic ortho esters under the same conditions. A mechanism is proposed which involves a branch point between the two products as the zwitterionic intermediate resulting from nucleophilic addition of the ketene acetal to the carbene carbon. A 1,3-migration of the methoxyl group to the cationic center leads to the ortho ester and a ring closure by backside attack leads to the cyclopropanone acetal. A double-labeling experiment shows that the 1,3-migration occurs by an intramolecular process that is proposed to involve a bridging oxonium ion. The effect of the isopropoxy group is thus interpreted to be to sterically hinder the formation of a bridged oxonium ion.     

A new method for the synthesis of bicyclic pyran acetals

cis‐Fused bicyclic acetals were obtained from the unusual cyclization reaction between diols and dihydropyran. Furothiopyran, substituted pyranopyrans, and pyranooxepine and pyranobenzoxepine compounds were obtained with high diastereoselectivity and cis‐diastereomers were obtained in high yields.     

One-pot synthesis of telluroketene acetals and haloketene acetals using sp2 geminated hetero organobismetallic intermediates

A novel one-pot synthesis of 1,1-dihalo-1-alkenes and 1,1-bis(butyltelluro)-1-alkenes was developed from hydrozirconation of alkynylzinc bromide with Cp₂Zr(H)Cl and subsequent capture of the Zn/Zr 1,1-heterodimetallo-1-alkene intermediates with halogen and tellurium electrophiles. These protocols, which include multiple reactions in a one-pot procedure, allow the preparation of the potentially useful haloketene acetals and telluroketene acetals from terminal alkynes, under mild conditions and in a good yield.     

A selective convenient ruthenium-mediated synthesis of mixed acetals

Addition of alcohols and phenols to allyl ethers catalyzed mainly by ruthenium complexes was studied. Complexes of ruthenium generated in situ from precursors such as {[RuCl₂(1,5-COD)]_x} or [Ru₃(CO)₁₂] and from external ligands such as phosphines (e.g. PPh₃, PBu₃, BINAP) or phosphites (e.g. P(OPh)₃, P(OMe)₃) were found to be particularly efficient catalysts of the studied reactions. Transacetalization reaction could be practically completely eliminated by the addition of a base (particularly Na₂CO₃) to the catalytic systems. It was observed that the selectivity of mixed acetals formation increases with increasing value of Θ parameter of phosphines. Especially interesting results (0–5% of transacetalization) have been obtained for catalytic systems generated from {[RuCl₂(1,5-COD)]_x} or [Ru₃(CO)₁₂], phosphines (PPh₃, BINAP, dppe, tris(2,4,6-tri-metylphenyl)phosphine, or dppf) and Na₂CO₃. The mechanism of mixed acetals formation has been investigated using deuterated reagents. It is postulated that the examined reaction is a nucleophilic addition of ROH to a hydrido-π-allyl complex formed during oxidative addition of allyl substrate to metal complex. As a result, a new, selective, and convenient method of the synthesis of symmetrical and, in particular, unsymmetrical (mixed) acetals has been developed. Mixed acetals CH₃CH₂CH(OR¹)(OR²) may be obtained in the reaction of R¹-O-allyl with R²OH or R¹OH with R²-O-allyl, depending on the structure of R¹ and R².     

Thermal and palladium-catalyzed [3 + 2] synthesis of cyclopentadienone acetals from cyclopropenone acetals and acetylenes

[reaction: see text] Substituted cyclopentadienone acetals (CPDAs) were synthesized by a thermal or palladium-catalyzed [3 + 2] cycloaddition reaction of a substituted cyclopropenone acetal to an electron-deficient acetylene. The synthesis afforded di-, tri-, and tetra-substituted CPDAs of considerable structural varieties that undergo Diels-Alder reaction to produce bicyclo[2.2.1]heptenes.     

Expeditious synthesis of sulfoazetidine spiro-C-glycosides from ketose acetals

Pyranoid and furanoid spiro-N-mesyl azetidines, a new type of water-soluble spiro-C-nucleoside, have been prepared from easily available sugar spiroacetals (or glycosyl cyanides). The synthetic pathway involves opening of the acetalic ring with trimethylsilylcyanide, reduction, formation of an N,O-dimesylate, cyclization with sodium hydride in anhydrous DMF, and O-deprotection.     

Electrochemical synthesis of aldehydes and acetals from α-phenylthiocarboxylic acid

α-Phenylthiocarboxylic acids were converted to the corresponding aldehydes or acetals with oxidative decarboxylation and desulfurization by electrolysis.     

Cyclopentane synthesis and annulation: Intramolecular radical cyclization of acetals

A general procedure for cyclopentane synthesis based on free-radical cyclization of thioacetals is described. This permits the rapid assembly, by intramolecular annulation, of various ring systems bearing useful functionality for use in total synthesis.     

Direct synthesis of acetals by rhodium catalysed hydroformylation of alkenes in the presence of orthoformate

The two catalyst precursors [Rh₂(μ-penicillamine)₂(CO)₄][OTf]₂ and [Rh₂(μ-cysteine)₂(CO)₄][OTf]₂ in the presence of 4 equivalents of P(OPh)₃ in triethyl orthoformate as solvent and reactant, permit the low pressure hydroformylation of various alkenes into the corresponding acetals. Apart from a few low-yield by-products resulting from isomerization of the substrates, the carbonylated products obtained directly and exclusively are acetals.     

Reactions of polyhydric phenols with nitrogen-containing acetals in the synthesis of polyphenols and heterocyclic compounds

The review systematizes and summarizes the data on the reactions of nitrogen-containing acetals with phenols. Both intra- and intermolecular reactions leading to acyclic, macrocyclic, and heterocyclic compounds are considered.     

Ruthenium(III) chloride-catalyzed chemoselective synthesis of acetals from aldehydes

A mild and chemoselective acetalization procedure for the protection of various aldehydes in the presence of ketones is described.