Ramaprasad Chakrabarti

Bio: Ramaprasad Chakrabarti is an academic researcher. The author has contributed to research in topics: Ethyl acetoacetate & Condensation. The author has an hindex of 3, co-authored 3 publications receiving 17 citations.

Direct asymmetric Michael reactions of cyclic 1,3-dicarbonyl compounds and enamines catalyzed by chiral bisoxazoline-copper(II) complexes.

Abstract: The catalytic direct Michael addition of cyclic 1,3-dicarbonyl compounds and enamines to unsaturated 2-ketoesters is presented. A series of different 4-hydroxycoumarins, 4-hydroxy-6-methyl-2-pyrone, 3-hydroxy-1H-phenalene-1-one, 2-hydroxy-1,4-naphthoquinone, 5,5-dimethyl-1,3-cyclohexanedione, and various enamines of cyclic 1,3-diketones all add to unsaturated 4-substituted 2-ketoesters in an enantioselective manner. The reaction is catalyzed by chiral bisoxazoline−copper(II) complexes and proceeds in the absence of base to afford Michael adducts in good to high yields and with up to 98% ee. The products formed are substructures found in skeletons of important biological and pharmaceutical molecules. The scope and potential of the new reaction are discussed as well as the mechanism for the catalytic enantioselective reaction.

The chemistry of coumarin derivatives, part 2. Reaction of 4-hydroxycoumarin with α,β-unsaturated aldehydes†

Abstract: 4-Hydroxycoumarin (= 4-hydroxy-2H-1-benzopyran-2-one) reacts with enals to give 1,2- or 1,4-addition products, depending on the nature and relative location of the substituents on the olefinic double bond (Scheme 2). The resulting adducts further react intra- or intermolecularly, affording dimeric coumarins or pyranocoumarins in the case of 1,2-addition and acetalic pyranocoumarins in the case of 1,4-addition. With enals bearing alkyl groups at C(β), 2H-pyrano[3,2-c]coumarins are the only products formed, and the reaction represents an easy and straightforward entry into this class of recently described biologically active natural products.