An organocatalytic asymmetric cascade Michael/hemiketalization/acyl transfer reaction between (E)-2-(2-nitrovinyl)phenols and 1,3-propanediones is disclosed. A cinchona alkaloid derived bifunctional thiourea catalyst was found to be the most effective for this reaction and provided the desired products in moderate to good yields with good to high enantioselectivities.
Herein, we employ unsaturated pyrazolones
in the Rauhut–Currier
reaction for the first time. A domino Rauhut–Currier cyclization
reaction has been developed between unsaturated pyrazolones and nitro-olefins.
The trisubstituted tetrahydropyrano[2,3-c]pyrazoles
were obtained in moderate to high yields with excellent diastereoselectivities.
A few applications including a synthesis of disubstituted tetrahydropyrano[2,3-c]pyrazole have been demonstrated. A preliminary catalytic
asymmetric version of this process was also studied with chiral DMAP
catalysts.
Intermolecular cross Rauhut‐Currier reactions have gained much importance in recent years. It has proved its importance through procedures involving various catalysts and resulting in complex structures with good regio‐ as well as stereo‐ selectivity. This review highlights the recent developments of these reactions, published in current years, involving both achiral and chiral catalysts to give products, having various utilities. In addition, the detailed mechanistic studies of the above‐mentioned reactions are also presented.
An organocatalytic asymmetric oxa-Michael Michael reaction has been developed employing 3-aryl-2-nitroprop-2-enol and alkylidene pyrazolones. This report contains the first utlization of 3-aryl-2-nitroprop-2-enol as O-nucleophile in enantioselective catalysis. With 10 mol% of quinine derived squaramide catalyst, moderate yields and excellent diastereomeric ratios as well as high to excellent enantioselectivities are obtained for a variety of spiro-tetrahydropyran-pyrazolones under mild reaction conditions.
Herein we report a catalytic asymmetric
inverse-electron-demand
Diels–Alder reaction between alkylidene pyrazolones and allyl
ketones. Allyl ketone gets activated by a bifunctional thiourea catalyst
and acts as a dienolate in this reaction. The trisubstituted tetrahydropyrano[2,3-c]pyrazoles were obtained in moderate to good yields with
high diastereo- and enantioselectivities. Few applications, including
a decarbonylation reaction, have been demonstrated.
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