An application of various oximes as nucleophiles in the asymmetric ring-opening (ARO) reaction of aza/ oxabicyclic alkenes resulting in cis-ARO products has been developed. The reaction was co-catalyzed by Pd(OAc) 2 and Zn(OTf) 2 with (R)-DIFLUORPHOS as the chiral ligand. This methodology exhibits broad substrate scope, functional group tolerance with high enantioselectivity. A synthetic application of this method has been demonstrated.[a] G.
The
enantioselective Friedel–Crafts addition of naphthols
with isatin-derived ketimines was developed with H8-BINOL-derived
chiral biaryl phosphoric acid. A wide range of isatin-derived ketimines
and naphthols were successfully applied and gave a series of chiral
3-amino-2-oxindoles in excellent yields with high optical purities.
Reduction of different unsaturated compounds by transfer hydrogenation (TH) has emerged as a more efficient methodology as compared to the classical method of using the molecular hydrogen both in industry and laboratory. Transfer hydrogenation is more advantageous in terms of safety and convenience. Alcohols, formic acid, esters, H2O, etc are the common molecules which are used as hydrogen donor in the transfer hydrogenation reaction. Primary alcohols namely methanol and ethanol were less explored as a hydrogen source in the TH reaction; probably due to the formation of aldehyde after dehydrogenation of these alcohols which are more reactive and may undergo side reactions. However, methanol and ethanol are cheap, easily available and easy to handle compounds. They can be easily obtained from biomass, coal, etc. Because of these advantages, chemists became more interested in the application of methanol and ethanol as hydrogen sources in the transfer hydrogenation reaction. In this review, we present an overview of the work reported by different groups on the transfer hydrogenation reactions with methanol and ethanol as the hydrogen sources.
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