A new and efficient method is described for the oxidative esterification of aromatic aldehydes with different types of alcohols such as primary, secondary, benzylic, allylic and cyclic alcohols and phenols using air as the simplest available oxidant and potassium cyanide in DMF under neutral conditions in high yields. The present method esterifies aldehydes with alcohols in 1:1 molar ratio with excellent chemoselectivity and avoids the use of an external oxidant beside 02 from air.
In spite of many reports in the literature concerning with oxidation of benzylic alcohols to carbonyl compounds with 2,3-dichloro-5,6- dicyanobenzoquinone (DDQ) in stoichiometric amounts or even more, we surprisingly found that benzylic alcohols are directly oxidized to oximes using a catalytic amount of DDQ in the presence of hydroxylamine hydrochloride under solvent-free conditions. The present tandem catalytic method can be efficiently used for preparation of oximes in the presence of some other functional groups with excellent chemoselectivity.
AUTHOR KEYWORDS: 2,3-dichloro-5,6-dicyanobenzoquinone; Alcohol; Oxime; Tandem synthesis INDEX KEYWORDS: Alcohols; Carbonyl compounds, 2 ,3-dichloro-5 ,6-dicyanobenzoquinone; Benzylic alcohols; Catalytic amounts; Catalytic methods; Chemo-selectivity; Hydroxylamine hydrochloride; Oxime; Solvent free conditions, Catalytic oxidation PUBLISHER: Korean Chemical Society
A catalyst-free, direct, high regio-, and chemo-selective method is reported for the facile conversion of a wide variety of epoxides to their corresponding 2-thiocyanatoalkyl alkanoates, which contain two important functional groups (ester and thiocyanate), using a mixture of tetrabutylammonium rhodanide ((n-Bu)4NSCN) and an aliphatic or aromatic carboxylic anhydride under neutral and solvent-free conditions.
A new method is described for the mild and high regioselective conversion of epoxides to β-chlcrohydrins in high yields even in the presence of alcohols, carboxylic acids, oximes, amides, thiols and tetrahydropyranyl ethers using chlorodiphenylphosphine (ClPPh2) under solvent-free and neutral conditions at room temperature and in short reaction times. In addition, some other functional groups such as carbon-carbon double bonds, ester groups and also phenyl ring that are present in the epoxide molecules remain intact in this method.
Aldoximes are immediately converted to their corresponding nitriles with a mixture of triphenylphosphine and 2,3dichloro-5,6-dicyanobenzoquinone in dichloromethane under neutral conditions at room temperature., Nitriles are also formed from the reaction of primary amides with this reagent in refluxing acetonitrile under neutral conditions.
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