Useful methods for the synthesis of isopropylidenes and their chemoselective cleavage

A catalytic amount of phosphotungstic acid (PTA) has been found to be a very effective catalyst for isopropylidenation of 1,2-diols and their deprotection at room temperature. The ease of handling, cost and activity of the catalyst, good to excellent yields and chemoselectivity for deprotection are some of the highlights of the reported method.     

Diadamantylation of dihydric phenols and their derivatives

Dihydric phenols and their monomethyl ethers were converted into diadamantyl derivatives by the reaction with 1-adamantanol in trifluoroacetic acid.     

Organocatalytic chemoselective monoacylation of 1,n-linear disulfonamides

Predominant monoacylation of 1,n-linear disulfonamides took place in the presence of pyrrolidinopyridine-type organocatalysts when the chain length of the linear disulfonamides was n = 3, 4, or 5 (monoacylate/diacylate = up to 44). The chemoselectivity of the competitive acylation between N,N′-ditosyl-1,5-pentanediamine (n = 5) and N,N′-ditosyl-1,3-propanediamine (n = 3) was found to be 36, favoring the former substrate. Different chain length by only one carbon atom was discriminated in the competitive acylation between N,N′-ditosyl-1,5-pentanediamine (n = 5) and of N,N′-ditosyl-1,4-butanediamine (n = 4) with the relative acylation rate of 16 in the presence of the organocatalyst.     

Hydroxylation of substituted diatomic phenols and their derivatives

Oxidation of 3,6-di-tert-butylpyrocatechol in protic media is accompanied by the formation of 3,6-di-tert-butyl-2-hydroxy-para-benzoquinone. Hydroxylation of the 3,5-isomer results in dealkylation and isomerization with the formation of 6-tert-butyl-2-hydroxy-para-benzoquinone and the quinone mentioned above, respectively. Their ratio depends on the nature of the solvent. Analogous processes accompany redox transformations of 2,6-di-tert-butylhydroquinone, 2,6-diphenyl-para-benzoquinone, and 2,4,6-tri-tert-butylphenol adsorbed on silica gel. Derivatives of 3,5-substituted pyrocatechols formed under conditions of heterophase oxidation in air are capable of transformations to form nitrogen-containing compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2007–2010, October, 1998.     

Exchange equilibria of substituted phenols and their O-tricyclohexylstannyl derivatives

Conclusions Investigations of metal-proton exchange equilibria using m- and p-substituted phenols and their tricyclohexylstannyl derivatives in CHCl₃ or C₅H₅N have shown that the polar effects of the substituents mainly destabilize the less polar H-O bond when compared with the more polar Sn-O.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2298– 2301, October, 1987.     

Phosphinated phenols from acid‐fragmentation of bisphenols and their unsymmetrical diamine derivatives for copolyimides

Four novel diamines (9–12) were prepared by a two‐step procedure from phosphinated phenols (1–4) that were prepared from acid‐fragmentation of four bisphenols, including bisphenol A, 4,4′‐isopropylidenebis(2,6‐dimethylphenol), cis(4‐hydroxyphenyl)cyclohexane, and 9,9′‐bis(4‐hydroxyphenyl)fluorene, followed by nucleophilic addition of 9,10‐dihydro‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO). Copolyimides based on (9–12) /4,4′‐diaminodiphenyl ether (ODA)/dianhydride were prepared. The structure‐property relationship on the copolyimides was discussed. Due to the structural similarity, (9) /ODA‐based copolyimides were compared with (10) /ODA‐based copolyimides, while (11) /ODA‐based copolyimides were compared with (12) /ODA‐based copolyimides. The dimethyl substitutents cause (10) /ODA‐based copolyimides to display higher T_g, modulus, dimensional stability, contact angle, and better solubility than (9) /ODA‐based copolyimides. (12) /ODA‐based copolyimides that exhibit fluorene moieties display higher T_g and thermal stability, but a lower contact angle and poorer solubility than (11) /ODA‐based copolyimides that exhibit cyclohexane moieties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 390–400     

Organocatalytic enantioselective Friedel-Crafts alkylation of simple phenols with trifluoropyruvate

Enantioselective Friedel-Crafts alkylation of simple phenols (4a-j) with 3,3,3-trifluoropyruvate (3) was accomplished by using chiral cinchona alkaloid catalyst 2h (10 mol %). High yields and enantioselectivities (71-94% ee) of the Friedel-Crafts alkylation products were obtained.     

An efficient chemoselective etherification of phenols in polyfunctional aromatic compounds

A simple and efficient chemoselective alkylation of phenols in polyfunctional aromatic compounds with different alkyl halides in the presence of K₂CO₃/TBAB is reported. The method is successful with various hydroxy aromatic acids or oximes possessing other functional groups.     

Reactions of α-trifluoromethyl-β-chloroethylsulfenyl chloride with phenols and their derivatives

In the absence of a catalyst, -trifluoromethyl--chloroethylsulfenyl chloride reacts electrophilically with ortho-para-substituted phenols bearing substituents of the first type. The reaction conditions are determined by the C-nucleophilic properties of the phenol, and the selectivity by solvent effects. These -trifluoromethyl--chloroethylthiolated phenols are shown to be highly prone to dehydrochlorination.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 832–837, April, 1990.     

Tandem and chemoselective synthesis of benzil derivatives from styrene and arene diazonium salts

A facile and practically applied protocol for synthesis of benzil derivatives using styrene and arene diazonium salts is reported. Pd(OAc)₂/SeO₂ catalytic system was found to be efficient for chemoselective synthesis of benzil. Selenium dioxide works well as an oxidant under milder reaction conditions. Moderate to very good yields of the desired products were obtained.     

Rapid and efficient chemoselective and multiple sulfations of phenols using sulfuryl imidazolium salts

Phenolic sulfates protected with a trichloroethyl or trifluoroethyl group were rapidly and efficiently obtained by reacting phenols with sulfuryl imidazolium salts in the presence of DBU. Phenolic hydroxyl groups could be sulfated in good yield in the presence of aliphatic hydroxyl groups and multiple sulfations were also readily achieved.     

Liquid-liquid and solid-phase extractions of phenols from virgin olive oil and their separation by chromatographic and electrophoretic methods

The high oxidative stability of virgin olive oil is related to its high monounsaturated/polyunsaturated ratio and to the presence of antioxidant compounds, such as tocopherols and phenols. In this paper, the isolation of phenolic compounds from virgin olive oil, by different methods, was tested and discussed. Particularly liquid-liquid and solid-phase extraction methods were compared, assaying, for the latter, three stationary phases (C8, C18 and Diol) and several elution mixtures. Quantification of phenolic and o-diphenolic substances in the extracts was performed by the traditional Folin-Ciocalteau method and the sodium molybdate reaction, respectively. Furthermore, the quantification of phenolic compounds in the extracts and in a standard mixture was carried out both with diode array and mass spectrometric detection and capillary zone electrophoresis.     

Organocatalytic Michael addition of aldehydes to vinyl sulfones: enantioselective alpha-alkylations of aldehydes and their derivatives

Organocatalytic asymmetric Michael reaction of unmodified aldehydes to vinyl sulfones catalyzed by silylated biarylprolinol afforded the desired Michael products with exceptional enantioselectivity. The described enantioselective addition to vinyl sulfones, in combination with desulfonation, offers a unique, asymmetric entry to alpha-alkylated aldehydes and their derivatives.     

A convenient synthesis of dihydrocoumarins from phenols and cinnamic acid derivatives

A facile procedure for synthesis of dihydrocoumarin derivatives was described. Although the yield of the products in the reaction of phenols with acrylates in trifluoroacetic acid in the presence of Pd(OAc)₂ giving coumarins was found to be very low, dihydrocoumarin derivatives were obtained in good to high yields in the absence of Pd(OAc)₂ when ethyl cinnamates bearing electron-donating groups were employed in this reaction.     

Nanocrystalline TiO_2 as an efficient and reusable catalyst for the chemoselective trimethylsilylation of primary and secondary alcohols and phenols

Nanocrystalline TiO₂ was used as an efficient and recyclable catalyst for the chemoselective trimethylsilylation of primary and less hindered secondary alcohols and phenols with hexamethyldisilazane（HMDS）.All reactions were performed under mild and completely heterogeneous conditions in good to excellent yields.