The selectivity of a three-component electrophilic reaction of an aldehyde with dimedone and another carbon-based nucleophile could be improved by a reversible alkylation procedure, which involves formation, breaking and regeneration of C-C bonds. In the presence of iron(III) chloride and triphenylphosphine, an analogous C-C bond breaking can be observed in the reaction of 2,3,4,9-tetrahydro-9-(2-hydroxy-4,4-dimethyl-6-oxo-1-cyclohexen-1-yl)-3,3-dimethyl-1H-xanthen-1-one, in which the fragment of dimedone was replaced by a carbon-based nucleophile. Inspired by this observation, some three-component reactions of salicyldehyde and dimedone were successfully developed by using iron(III) chloride and triphenylphosphine (PPh3) as catalyst. PPh3 plays the role of hydrogen bond acceptor, which confers a good flexibility of the substrate by weakening the intramolecular hydrogen bond, allowing thus an easy interaction of the substrate with iron(III) chloride catalyst.
Using moelcular oxygen as the terminal oxidant, various aryl halide-containing b-aryl ketones and aldehydes can be synthesized directly from readily available allyic alcohols and boronic acids via palladium-catalyzed oxidative cross-coupling reactions. The dual roles of copper, including electron-carrier and Lewis acid functions, are supposed to be critical for the high reactivity and selectivity of this aerobic oxidative coupling transformation.
A series of sulfonic acid-functionalized (SO3H-functionalized) ionic liquids was synthesized and used as metal-free, highly selective and efficient catalysts for the direct amination of alcohols. Notably, the activities of the series of SO3H-functionalized ionic liquids were compared and a 92% isolated yield was obtained using 3-tetradecyl-1-(butyl-4-sulfonyl)imidazolium trifluoromethanesulfonate (BsTdIM]OTf]) as the catalyst. Importantly, the catalytic system has wide substrate scope including benzylic, allyl, propargylic, aliphatic alcohols with sulfonamide, amide, carbamate, aromatic amine and N-heterocyclic compounds. Interestingly, the system was also suitable for a multi-gram scale direct amination of alcohols. Additionally, the reusable nature of BsTdIM]OTf] makes this protocol more attractive and avoids the disposal and neutralization of acidic catalysts. Moreover, preliminary experiments indicated that this reaction should proceed via an SN1 pathway.
The direct C-H benzylation of azoles with benzyl chlorides proceeds efficiently, via sequential cleavage of one sp2 C-H bond and two sp3 C-H bonds in the presence of a palladium catalyst, to generate a wide range of tribenzylated azoles with a quaternary carbon center efficiently. The same catalyst could also promote the mono- and dibenzylation reactions through fine turning of the base and reaction conditions.
The Lewis acid-catalyzed conjugate addition of 2-alkylazaarenes to methylenemalononitriles through sp3 C-H bond functionalization has been developed, which provides an efficient and reliable method for incorporation of the nitrile group into the heterocycles.