Fluorescent cyclodextrins as chemosensors for the detection of cyclic and acyclic alcohols

Molecular sensing abilities and selectivities of a “turn-on” chemosensor, NBDamine-appended α-cyclodextrin (NC0αCD), were studied for cyclic alcohols and acyclic alcohols. This chemosensor is more sensitive to cyclic alcohols than acyclic alcohols, although its binding affinity is stronger for acyclic alcohols than cyclic alcohols.     

Palladium-catalyzed oxidation of alcohols via their allyl carbonates under neutral conditions

Treatment of alkyl allyl carbonates derived from various alcohols with a palladium catalyst in MeCN affords ketones and aldehydes in high yields. This new method of oxidation of alcohols can be applied to various alcohols except simple primary alcohols.     

CuCl catalyzed selective oxidation of primary alcohols to carboxylic acids with tert-butyl hydroperoxide at room temperature

Direct oxidation of primary alcohols to the corresponding carboxylic acids is performed highly efficiently at room temperature with anhydrous tert-butyl hydroperoxide in the presence of a catalytic amount of easily available CuCl under ligand free conditions in acetonitrile. Benzylic alcohols are more reactive than aliphatic alcohols, and these benzylic alcohols are selectively oxidized to the corresponding acids in the presence of aliphatic alcohols such as 1-octanol and 1-decanol.     

N-溴代丁二酰亚胺水相氧化醇类化合物反应研究

以水为反应介质、NBS为氧化剂,在水相无催化剂条件下实现了醇的氧化.芳香醇、脂肪醇都可以达到95%以上的醛(或酮)产率,但该体系对一些含供电子取代基的醇的反应活性不高,选用salen-Co(Ⅲ)配合物作为催化剂,可拓宽反应的底物适用范围.     

Recent developments in non-enzymatic catalytic oxidative kinetic resolution of secondary alcohols

The goal of this review is to collect the recent developments in non-enzymatic catalytic oxidative kinetic resolutions of secondary alcohols reported since the beginning of 2011. It is divided into four sections, dealing successively with manganese-catalysed oxidative kinetic resolutions of secondary alcohols, palladium-catalysed oxidative kinetic resolutions of secondary alcohols, oxidative kinetic resolutions of secondary alcohols catalysed by other metals and organocatalysed oxidative kinetic resolutions of secondary alcohols.     

Copper-catalyzed arylation of beta-amino alcohols

[reaction: see text] Methods for synthesizing N-aryl beta-amino alcohols and O-aryl beta-amino alcohols are described. The presence of a neighboring hydroxyl or amino group, respectively, is thought to activate beta-amino alcohols toward these transformations. These protocols significantly increase access to a variety of arylated beta-amino alcohols.     

Synthèse d'alcools acétyléniques par alkylation d'hydroxy-ω-alkynes-1

Synthesis of acetylenic alcohols by alkylation of ω-hydroxy-1-alkynes In liquid ammonia and with lithium amide, the alkylation of an ω-hydroxyl-alkyne proceeds with good yield with primary or secondary alcohols and with fair yield with tertiary alcohols. It is a very convenient way to prepare many substituted acetylenic alcohols.     

Synthetic scope of Ru(OH)x/Al2O3-catalyzed hydrogen-transfer reactions: an application to reduction of allylic alcohols by a sequential process of isomerization/Meerwein-Ponndorf-Verley-type reduction

Reduction of allylic alcohols can be promoted efficiently by the supported ruthenium catalyst Ru(OH)x/Al2O3. Various allylic alcohols were converted to saturated alcohols in excellent yields by using 2-propanol without any additives. This Ru(OH)x/Al2O3-catalyzed reduction of a dienol proceeds only at the allylic double bond to afford the corresponding enol, and chemoselective isomerization and reduction can be realized under similar conditions. The catalysis is truly heterogeneous and the high catalytic performance can be maintained during at least three recycles of the Ru(OH)x/Al2O3 catalyst. The transformation of allylic alcohols to saturated alcohols consists of three sequential reactions: oxidation of allylic alcohols to alpha,beta-unsaturated carbonyl compounds; reduction of alpha,beta-unsaturated carbonyl compounds to saturated carbonyl compounds; and reduction of saturated carbonyl compounds to saturated alcohols.     

Selective oxidation of benzylic and allylic alcohols using Mn(OAc)3/catalytic 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

A practical, chemoselective oxidation of alcohols employing catalytic quantities of DDQ as the oxidant and Mn(OAc)(3) as the co-oxidant is described. Electron-rich benzylic alcohols are oxidized efficiently to their corresponding carbonyls, but less electron-rich benzylic alcohols remain unchanged. Allylic alcohols are rapidly oxidized to their corresponding aldehyde or ketone counterparts in high yields. This protocol is operationally simple, employs an inexpensive source of Mn(OAc)(3), has short reaction times, and exhibits a significant chemoselectivity favoring allylic alcohols over benzylic alcohols. This procedure also avoids the use of very large excesses of reagents and sometimes poor reproducibility that characterize previously developed reagents such as MnO(2).     

Studies on the Cu(I)-catalyzed regioselective anti-carbometallation of secondary terminal propargylic alcohols

A highly regioselective Cu(I)-catalyzed anti-carbometallation of secondary terminal propargylic alcohols with 1 degrees alkyl or aryl Grignard reagents affording 2-substituted allylic alcohols was developed. By using this method, optically active allylic alcohols can be prepared from the optically active propargylic alcohols without obvious loss of the enantiopurity. The cyclic organometallic intermediate formed may undergo an iodination or a Pd(0)-catalyzed coupling reaction to afford stereo-defined allylic alcohols.     

Oxone/Sodium Chloride: A Simple and Efficient Catalytic System for the Oxidation of Alcohols to Symmetric Esters and Ketones

An efficient method for the oxidation of alcohols is presented. The use of catalytic amounts of sodium chloride in combination with oxone allows the conversion primary aliphatic alcohols to symmetric esters. Secondary alcohols can be easily oxidized to ketones, and benzylic alcohols are converted to the corresponding aldehydes. The method is cost effective and enviromentally benign.     

N-thioacyl 1,3-amino alcohols: synthesis via ring-opening of oxiranes with thioamide dianions and applications as key intermediates leading to stereochemically defined 5,6-dihydro-4H-1,3-oxazines and 1,3-amino alcohols

N-Thioacyl 1,3-amino alcohols were synthesized via the ring-opening of oxiranes with thioamide dianions generated from N-benzyl thioamides and BuLi in a highly regio- and stereoselective manner. The diastereomers of N-thioacyl 1,3-amino alcohols were readily separated by column chromatography to give stereochemically defined N-thioacyl 1,3-amino alcohols. They underwent intramolecular cyclization with Bu4F and EtI to give 5,6-dihydro-4H-1,3-oxazines. The reaction was specific with anti-N-thioacyl 1,3-amino alcohols, and cis-5,6-dihydro-4H-1,3-oxazines were obtained with high efficiency, whereas the reaction of a syn-alcohol gave a thioimidate as a major product. The reduction of N-thioacyl 1,3-amino alcohols with LiAlH4gave N-alkyl 1,3-amino alcohols in high yields. The use of optically active propylene oxide as a starting material gave the corresponding oxazine and alcohols in optically pure forms.     

Facile One-pot Transformation of 2,3-Epoxy Alcohols into Allylic Alcohols

Optically-active allylic alcohols have been frequently used as chiral building blocks for the preparation of optically pure compounds.¹ There are at present various methods for the synthesis of optically active allylic alcohols including the kinetic resolution racemic allylic alcohols,² reductive rearrangement of 2,3-epoxy alcohol by metal, halide and telluium-based chemistry.³ To our knowledge, One-pot Transformation of 2,3-epoxy alcohols into allylic alcohols, especially via epoxy iodides,is limited to Dorta's method³ using a Ph₃P,iodine, imidazole,2,6-lutidine and water system. The original Dorta's method can be successfully applied to the formation of tertiary allylic alcohols, but give unsatisfactory results in formation of secondary allylic alcohols.     

Probing the specificity of the S1′, leaving group,site of subtilisin Bacillus lentus using an enzyme-catalyzed transesterification reaction

Subtilisin Bacillus lentus catalyzes transesterifications between N-acetyl-L-phenylalanine vinyl ester and a wide range of alcohols. Reaction yields are high when primary alcohols are used, and quantitative with methanol. With chiral alcohols, the reaction is enantioselective, and the stereoselectivity is reversed on going from open chain secondary alcohols to β-branched primary alcohols. A model is proposed to account for this change in absolute configuration preference.     

Efficient transesterification/acylation reactions mediated by N-heterocyclic carbene catalysts

Imidazol-2-ylidenes, a family of N-heterocyclic carbenes (NHC), are efficient catalysts in the transesterification involving numerous esters and alcohols. Low catalyst loadings of aryl- or alkyl-substituted NHC catalysts mediate the acylation of alcohols with enol acetates in short reaction times at room temperature. Commercially available and more difficult to cleave methyl esters react with primary alcohols in the presence of alkyl-substituted NHC to efficiently form the corresponding esters. While primary alcohols are selectively acylated over secondary alcohols with use of enol esters as acylating agents, methyl and ethyl esters can be employed as protective agents for secondary alcohols in the presence of the more active alkyl-substituted NHC catalysts. The NHC-catalyzed transesterification protocol was simplified by generating the imidazol-2-ylidene catalysts in situ.     

Efficient and Highly Selective Oxidation of Primary Alcohols to Aldehydes by N-Chlorosuccinimide Mediated by Oxoammonium Salts

2,2,6,6-Tetramethyl-1-piperidinyloxy catalyzes efficient oxidation of primary alcohols to aldehydes by N-chlorosuccinimide, in a biphasic dichloromethane-aqueous pH 8.6 buffer system in the presence of tetrabutylammonium chloride. Aliphatic, benzylic, and allylic alcohols are readily oxidized with no overoxidation to carboxylic acids. Secondary alcohols are oxidized to ketones with a much lower efficiency. Very high chemoselectivities are observed when primary alcohols are oxidized in the presence of secondary ones. Primary-secondary diols are selectively transformed into hydroxy aldehydes, with, in some cases, no detectable formation of the isomeric keto alcohols.     

β-Arylation of Racemic Secondary Benzylic Alcohols to Access Enantioenriched β-Arylated Alcohols

The transformation of alcohols into value-added products is of great importance, as simple alcohols are widespread and can be easily derived from both fossil fuels and biomass. The selective functionalization of a sp³ C−H bond on the alkyl side chain of an alcohol over its hydroxyl group would offer an expedient route to expand the chemical space of alcohols but it remains a challenging task. Harnessing the borrowing hydrogen strategy, the β-arylation of secondary alcohols with aryl bromides has been achieved in this study, which allows for the selective functionalization of a β-Csp³−H bond in an alcohol substrate. Under the catalysis of a Pd complex, secondary alcohols reacted with aryl bromides to afford 1,2-diaryl alcohols with broad substrate scope in the presence of a ketone additive. Furthermore, the enantioconvergent version of the reaction has also been realized, transforming racemic secondary alcohols into enantioenriched chiral 1,2-diaryl alcohols under the cooperative Pd and Ru catalysis. Mechanism studies indicate that the reactions are enabled by borrowing hydrogen catalysis.     

Widely useful DMAP-catalyzed esterification under auxiliary base- and solvent-free conditions

With regard to atom economy and E-factor, catalytic condensation of carboxylic acids with equimolar amounts of alcohols is the most desirable. Although several highly active dehydration catalysts have been reported, more efficient alternatives are still strongly needed because the dehydrative esterification of tertiary alcohols, phenols, acid-sensitive alcohols, amino acids, and hardly soluble alcohols has never proceeded satisfactorily. Here we report new insights into the classical DMAP-catalyzed acylation of alcohols: surprisingly, only a 0.05-2 mol % of DMAP can efficiently promote acylation of alcohols with acid anhydrides under auxiliary base- and solvent-free conditions to give the corresponding esters in high yields. Furthermore, we achieved the recovery and reuse of commercially available polystyrene-supported DMAP without using any solvents. These serendipitous findings provide widely useful and environmentally benign esterification methods, which might be more practical and reliable than catalytic dehydrative condensation methods, in particular, for the less reactive alcohols which hardly condense with carboxylic acid directly.     

Isomerization reactions of allylic alcohols into ketones with the Grubbs reagent

Allylic alcohols were isomerized into ketones by the action of the Grubbs reagent. Some model alcohols were prepared and tested under similar conditions to reveal that less substituted alkenes rearrange more easily. More hindered alcohols are stable under these conditions, however, the simple allylic alcohols tend to isomerize producing ethyl ketone and the corresponding degraded methyl ketone.     

Glucosidation shifts of allylic and benzylic alcohols in 13C NMR spectroscopy

The ¹³C FT NMR spectra of β-D -glucopyranosides (including their tetraacetates) of several secondary allylic and benzylic alcohols were compared with those of methyl β-D -glucopyranoside and the corresponding parent alcohols. The characeristic glucosidation shifts observed for these alcohols may be applicable to the determination of the absolute configuration of the hydroxy group in these alcohols.