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A new method for the generation of benzyl radicals from acetals via low-valent titanium-mediated homolytic CO bond cleavage is presented. The low cost and availability of the developed titanium reagent enable efficient access to α-alkoxy carbon radical species via the developed reaction.

The first silver-catalyzed reaction of acetals or ketals with diazoesters leading to trisubstituted or tetrasubstituted β-alkoxyacrylates is now reported. A broad range of acetals and ketals bearing different substituents is compatible with this protocol and thus provides an attractive approach for the synthesis of complex β-alkoxyacrylates. The power of this method was further demonstrated by the successful synthesis of picoxystrobin, which is one of the most popular agricultural fungicides commercialized by Dupont.

A fluorinated cobalt(III) porphyrin complex [Co(TPFPP)-NTf2·2C2H5OH, where TPFPP=5,10,15,20-tetrakis(penta-fluorophenyl)porphyrin, Tf=CF3SO2] promotes hydroalkoxylation of alkynes to give acetals in good to excellent yields. The acetals can be directly functionalized with nucleophiles in a one-pot procedure.

Aldehydes and ketones are readily protected in the presence of trialkyl orthoformate and a catalytic amount of cerium(III) trifluoromethanesulfonate under mild conditions to give the corresponding acetals in good to excellent yields. Due to the mild reaction conditions, this method is compatible with acid-sensitive substrates. Copyright

Investigation of the solvent and alkoxide precursor effect on the nonhydrolytic sol-gel synthesis of oxide nanoparticles by means of an ether elimination (Bradley) reaction indicates that the best crystallinity of the resulting oxide particles is achieved

Aldehydes and ketones can be protected as acetals and ketals by treatment with trimethyl orthoformate (TMOF) or triethyl orthoformate (TEOF) under the catalytic influence of tetrafluoroboric acid adsorbed on silica gel (HBF 4-SiO2). In the case of aldehydes or ketones with highly electrophilic carbonyl group, the reactions are carried out under solvent-free conditions. Aryl alkyl ketones, aryl styryl ketones, aldehydes with weakly electrophilic carbonyl groups, and aldehydes with substituents that can coordinate with the catalyst require the presence of the corresponding alcohol as solvent. For substrates that can be converted into acetals under neat conditions, the acetal formation takes place at a faster rate when the alcohol is used as the solvent. The catalyst can be recovered and reused/recycled four times (after reactivation after each use) without any significant decrease in its catalytic efficiency. The parent aldehydes/ketones are regenerated from the corresponding acetals/ketals in high yields by the treatment with water-alcohol in the presence of HBF4-SiO2 at room temperature for short times. Excellent selectivity was observed during inter- and intramolecular competition studies involving carbonyl substrates with varying electronic and steric environments. Selective acetal formation of benzaldehyde takes place in the presence of 4-(dimethylamino)benzaldehyde, thiophene-2-carboxaldehyde, 1-naphthaldehyde, 9-anthraldehyde, or acetophenone, but 3-nitrobenzaldehyde undergoes selective acetal formation in preference to benzaldehyde. In the case of 4-acetylbenzaldehyde, exclusive acetal formation of the aldehyde carbonyl group occurs. Georg Thieme Verlag Stuttgart.

Diethyl acetals were obtained from carbonyl compounds in good to excellent yields under mild reaction conditions in the presence of triethyl orthoformate and a catalytic amount of gallium triiodide in anhydrous ethanol.

An efficient method for conversion of ketones to their corresponding dimethyl and diethyl acetals and of cyclic β-diketones into β-keto enol ethers using Fe(OTs)3 as a catalyst is described. Copyright Taylor & Francis Group, LLC.

Perchloric acid adsorbed on silica gel (HClO4-SiO2) is reported as extremely efficient, inexpensive, and reusable catalyst for dual role for protection of aldehydes/ketones (with trialkyl orthoformates) as acetals/ketals and deprotection (with water-alcohol) to regenerate the carbonyl compounds in high yields at room temperature and in short times. Acetalization/ketalization of electrophilic aldehydes/ketones was carried out under solvent-free conditions. Weakly electrophilic aldehydes/ketones and aldehydes having a substituent that can coordinate with the catalyst, required the corresponding alcohol as solvent. Georg Thieme Verlag Stuttgart.

Pd[(-)-sparteine]Cl2 catalyzes the formation of dialkyl acetals from styrene derivatives with Markovnikov regioselectivity. The substrate scope of this reaction has been investigated, and initial mechanistic studies indicate that the reaction proceeds through an enol ether intermediate and a Pd-hydride.

The acid-free, organocatalytic acetalization of various aldehydes and ketones with N,N′-bis[3,5-bis(trifluoromethyl)phenyl]thiourea is presented. The neutral, double hydrogen bonding thiourea catalyst can be used at very low loadings of 0.01-1 mol% at room temperature to furnish the respective acetals in 65-99% yield at turnover frequencies around 600 h-1. Acid-labile TBDMS-protected as well as unsaturated aldehydes can be converted efficiently into their acetals utilizing this very mild and highly practical method.

A series of acidic ionic liquids have been used as efficient catalysts for the protection of various carbonyl compounds at room temperature. The features of mild conditions, satisfactory isolated yield, simple workup, and the recyclability of the catalyst were present in this process. Copyright Taylor & Francis, Inc.

Commercially available copper(II) tetrafluoroborate hydrate has been found to be a highly efficient catalyst for dimethyl/diethyl acetal formation in high yields from aldehydes and ketones by reaction with trimethyl/triethyl orthoformate at room temperature and in short period. Acetalisation was carried out under solvent-free conditions with electrophilic aldehydes/ketones. For weakly electrophilic aldehydes/ketones (e.g., benzaldehyde, cinnamaldehyde and acetophenone) and for aldehydes having a substituent that can coordinate with the catalyst, the corresponding alcohol was used as solvent.

An efficient H2NSO3H-catalyzed protection of various carbonyl compounds at room temperature was investigated. The features of mild conditions, cost-efficient catalyst, simple workup, and the recyclability of the catalyst were represented in this process.

Acetals are obtained in good to excellent yields by treatment of aldehydes and ketones with trialkyl orthoformate and the corresponding alcohol in the presence of a catalytic amount of lithium tetrafluoroborate. Due to the mild reaction conditions, this method is compatible with acid-sensitive substrates.

Various types of aldehydes and ketones could be converted to their corresponding diethyl acetals with triethylorthoformate in the presence of TiO2/SO42- solid superacid in good to excellent yield under mild reaction conditions.

The efficient and chemoselective preparation of acetals and ketals from carbonyl compounds, transacetalization reactions, the conversion of epoxides to acetonides, and the preparation of acylals from aldehydes in the presence of catalytic amounts of 2,4,4,6-tetrabromo-2,5-cyclohexadienone (TABCO) are described.

Acyclic and cyclic acetals of various carbonyl compounds were obtained in excellent yields under a mild reaction condition in the presence of trialkyl orthoformate and a catalytic amount of tetrabutylammonium tribromide (TBATB) in absolute alcohol. Chemoselective acetalization of an aldehyde in the presence of ketone, unsymmetrical acetal formation, shorter reaction times, mild reaction conditions, the stability of acid-sensitive protecting groups, high efficiencies, facile isolation of the desired products, and the catalytic nature of the reagent make the present methodology a practical alternative.

Highly efficient interconversion of a range of 1,3-oxathiolanes, 1,3-dithiolanes and 1,3-dithianes to their acetals at ambient temperature using N-bromosuccinimide or N-chlorosuccinimide and different types of alcohols and diols was investigated.

New routes to N-(diethoxyphosphoryl)imines derived from enolizable carbonyl compounds have been investigated. Three different procedures were studied: (i) the aza-Claisen condensation of ethyl-[N-(diethoxyphosphoryl)]-formimidate with enolizable ketones, (ii) the reaction between diethyl N-sulfinylphosphoramidate and aliphatic aldehydes, and (iii) the thermally induced reaction of diethyl phosphoramidate with ketone diethyl acetals. With two exceptions in all cases the products were identified as diethyl 1-alkenylphosphoramidates with no spectroscopically detectable amounts of imine tautomers. The aza-Claisen condensation can be recommended as a simple and effective route to diethyl 1-alkenyl-3-oxophosphoramidates. (C) 2000 Elsevier Science Ltd.

A regioselective reductive demethoxylation of alkyl methyl ketals employing sodium cyanoborohydride in the presence of a catalytic amount of tri-n-butyltin chloride as Lewis acid is described.

Various types of structurally different carbonyl compounds in the presence of ethyl orthoformate (EtO)3CH could be efficiently converted to their diethyl acetals by using a catalytic amount (1-3 mol%) of DDQ under mild reaction conditions.

Highly efficient and mild acetalization of various types of carbonyl compounds was achieved using NBS under almost neutral reaction conditions. Due to the neutrality of the medium this method is especially useful for the protection of acid sensitive substrates. Thieme Stuttgart.

Various types of aldehydes and ketones could be converted chemoselectively to their corresponding 1,3-dioxanes or diethyl acetals in the presence of catalytic amounts of tungsten hexachloride (WCl6) in good to excellent yields in CH2Cl2 or under neat conditions, respectively.

Zirconium tetrachloride (ZrCl4) is a highly efficient and chemoselective catalyst for the acetalization, and in-situ transacetalization of carbonyl compounds under mild reaction conditions.

Oxidation of C-aryl or alkyl-N-arylaldimines 6 or 20 by sodium perborate tetrahydrate (SPB) in trifluoroacetic acid solution gives rearranged N,N-disubstituted formamides 9 and 21. Yields are variable and solvent dependant with the best yields (50-60%) being obtained for electronically neutral C-aryl substituents or C-s-alkyl substituents. Product formation is rationalised in terms of an intermediate oxaziridine 5 that rearranges via acid catalysed O-N bond cleavage. An alternative C-O bond cleavage of these intermediates accounts for the formation of aldehydes, which are common by products. Rearrangement appears to be favoured by N-aryl substituents and by C-substituents that do not stabilise a developing positive charge on carbon. Further support for an oxaziridine intermediate 5 is provided by the observation that MCPBA oxidation of benzaldehyde phenylimine gives rearranged N,N-diphenylformamide. Under the conditions of the SPB oxidative rearrangements, oxaziridine formation may well occur by initial formation of trifluoroperacetic acid. Stereochemical aspects of this novel rearrangement of aldimines 1 → 2 have been investigated using trans- and cis-myrtanal 25 and 30. The observed epimerisation using die N-4-tolyl imine of trans-myrtanal 26 is believed to arise from equilibration of the precursor imine 26 with the tautomeric enamine 35b.

A one-flask conversion of cyclic ketones to N-methyl lactams is described. Reaction of the ketone with triethylorthoformate generates an acetal which is reacted in situ with N-(((p-nitrobenzene)sulfonyl)oxy methylamine 2a(CH3NH-OSO2C6H4NO2). Dealkylation of the resulting O-ethyl imidate with sodium iodide gives the lactam. A variety of lactams, including macrocyclic lactams, are produced simply and in good yields.

During the action of an anhydrous solution of perchloric acid in alcohol on methyl aryl ketones in ethyl orthoformate open-chain carboxonium salts (derivatives of the 1,5-diaryl-2-pentene-1,5-dione) were formed instead of the 2,6-diarylpyrylium perchlorat

The relationships governing the transformation of phenylacetylene in the presence of the HgO-BF3*O(C2H5)2 catalytic system were investigated.The reaction takes place by a cationic chain mechanism, and the main products from the transformation of phenylacetylene in alcohols are 1,1-dialkoxy-1-phenylethanes, acetophenone, dimeric termination products, 1,3,5-triphenylbenzene, and linear mercury-containing polymers.

A series of para- and meta-substituted acetophenones were prpared which were highly labeled with 18O at the carbonyl function.The natural abundance 13C NMR spectra of the compounds were recorded and the 18O-isotope-induced shifts of the carbonyl carbon we

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