Enhanced reactivity and selectivity of asymmetric oxa-Michael addition of 2′-hydroxychalcones in carbon confined spaces

Abstract

Carbon nanotubes (CNTs) are employed as nanoscale reaction vessels for the asymmetric oxa-Michael addition of 2'-hydroxychalcones. A systematic comparison of the catalytic activities of chiral phosphoric acid treated ferrite nanoparticles (chiral ferrites) has been studied for the synthesis of flavanones. Higher reactivity and selectivity with switching of enantiomers were observed when these chiral ferrites are inside the CNT channel.

Catalytic enantioselective synthesis of tetrasubstituted chromanones via palladium-catalyzed asymmetric conjugate arylation using chiral pyridine-dihydroisoquinoline ligands

“…Optically active chromanone scaffolds having a stereocenter at the C2 position are prominent structural motifs in natural products, and possess numerous bioactivities ( Scheme 1a ). 1 Chiral chromanones have been synthesized by various methods, 2 such as intramolecular oxa-Michael additions, 3 asymmetric conjugate additions, 4 asymmetric reductions, 5 and Mitsunobu cyclizations. 6 Nevertheless, much of the previous research has focused on generation of trisubstituted rather than tetrasubstituted stereocenters.…”

Recent Advances in Organocatalyzed Asymmetric Synthesis of Benzopyran and Benzodihydropyran (Chromane) Nuclei

“…Although it did not produce enantioenriched products, Wang, Bu and co-workers performed a highly diasteroselective triple cascade reaction (Michael addition/condensation/Friedel-Crafts) of 3indolyl-substituted oxindoles with ortho-hydroxychalcones (Scheme 8) [16,17]. The reaction yields were influenced by the bulkiness of the N-protecting group and the little methyl group was found to The reaction of ortho-hydroxystyrene and azlactone catalyzed by chiral BINOL-phosphoric acid with and without chiral guanidine as the co-catalyst was studied with the density functional theory method [14].…”

“…Although it did not produce enantioenriched products, Wang, Bu and co-workers performed a highly diasteroselective triple cascade reaction (Michael addition/condensation/Friedel-Crafts) of 3indolyl-substituted oxindoles with ortho-hydroxychalcones (Scheme 8) [16,17]. The reaction yields were influenced by the bulkiness of the N-protecting group and the little methyl group was found to Chiral 2-arylbenzopyranones (flavanones) can be obtained by the oxa-Michael reaction of 2 -hydroxychalcone or 1-(2-hydroxyaryl) α,β-unsaturated aliphatic ketones.…”

“…The reaction yields were influenced by the bulkiness of the N-protecting group and the little methyl group was found to Chiral 2-arylbenzopyranones (flavanones) can be obtained by the oxa-Michael reaction of 2 -hydroxychalcone or 1-(2-hydroxyaryl) α,β-unsaturated aliphatic ketones. In 2017, Ranganath and co-workers introduced heterogeneous catalysts prepared from magnetite and cobalt ferrite nanoparticles with a binaphthol phosphate as the chiral ligand [16]. The reaction presented two interesting features: higher enantioselectivity and the opposite configuration when the chiral ferrite nanoparticles were alone or in cobalt ferrite nanoparticles (Scheme 7).…”

Six-Membered Ring Systems: With O and/or S Atoms

“…3-(Propane-1,3-dione)pyridine N-oxides, prepared in two steps via base-catalyzed Claisen condensation of nicotinates with 1,2-disubstituted ethan-1-ones followed by oxidation with m-chloroperoxybenzoic acid, underwent intramolecular O-arylation under PyBrop (bromotripyrrolidinophosphonium hexafluorophosphate) or Ac 2 O activation conditions to afford a range of 8-aza-4H-chromen-4-ones (Scheme 70; Asymmetric oxa-Michael addition of 2 0 -hydroxychalcones catalyzed by CPAs modified magnetite nanoparticles inside and outside carbon nanotubes leads to 2-substituted 4H-chroman-4-ones (17CC6029). Other analogs arise from palladium(II)-mediated [3þ3] annulation of vinyl chromium(0) Fischer carbene complexes with 2-iodophenols (Scheme 71).…”