Péter Bakó

Asymmetric C–C bond forming reactions with chiral crown catalysts derived from d-glucose and d-galactose

Abstract New chiral monoaza-15-crown-5 derivatives anellated to methyl-4,6-O-benzylidene-α- d -glucopyranoside 2a, 2e, 2g–i and to methyl-4,6-O-benzylidene-α- d -galactopyranoside 3a, 3e, 3i have been synthesized. These crown ethers showed significant asymmetric induction as phase transfer catalysts in the Michael addition of 2-nitropropane to chalcone (87% ee), in the Darzens condensation of phenacyl chloride with benzaldehyde (71% ee) and in the self-condensation of phenacyl chloride (64% ee) to give 14. The absolute configurations of (−)-(2R,3S)-epoxy-3-(4-chlorophenyl)-1-phenyl-1-propanone 12 and (−)-4-chloro-(2R,3S)-epoxy-1,3-diphenyl-1-butanone 14 have also been determined by X-ray diffraction.

Enantioselective Michael reaction of 2-nitropropane with substituted chalcones catalysed by chiral azacrown ethers derived from α-D-glucose

Abstract The chiral monoaza-15-crown-5 lariat ethers anellated to methyl-4,6-O-benzylidene-α- d -glucopyranoside 1a–c showed significant asymmetric induction as phase transfer catalysts in the Michael addition of 2-nitropropane to substituted chalcones. Among the catalysts bearing different side arms at the nitrogen atom, the compound with a phosphinoxidoalkyl side chain 1c proved to be the most effective (max. 78% e.e.). The type of substituent on the chalcone was found to have a very significant influence on both the chemical yield and the enantioselectivity of the reaction. The absolute configuration of the Michael adducts 3b and 3i was determined by chemical methods, while that of 3d was assigned by X-ray crystal structure determination.

d-Glucose-based azacrown ethers with a phosphonoalkyl side chain: application as enantioselective phase transfer catalysts

Abstract Five chiral α- d -glucose-based monoaza-15-crown-5 ethers with a phosphonoalkyl side chain 5a – e have been synthesized. The substituent at the nitrogen atom has a major influence on the cation extraction ability of the azacrown. The new lariat ethers 5a – e show significant asymmetric induction as phase transfer catalysts in the Michael addition of 2-nitropropane to chalcone.

Chiral azacrown ethers derived from D-glucose as catalysts for enantioselective Michael addition

Abstract Chiral monoaza-crown ethers incorporating glucose units have been synthesized and applied as phase transfer catalysts in the enantioselective Michael addition of 2-nitropropane to a chalcone to give the corresponding adduct in enantiomeric excess up to 90%.

Enantioselective Michael addition of 2-nitropropane to chalcone analogues catalyzed by chiral azacrown ethers based on α-d-glucose and d-mannitol

Abstract The chiral monoaza-15-crown-5 type lariat ethers 1 and 2 derived from α- d -glucose and from d -mannitol, respectively, have been applied as phase transfer catalysts in the enantioselective Michael addition of 2-nitropropane to aromatic 3b–c and heteroaromatic 3d–h chalcone analogues. Among the catalysts, the glucose-based 1c with a phosphinoxidobutyl side arm proved to be the most effective, it inducing 34% e.e. for 4b, 59% e.e. for 4c, 80% e.e. for 4d, 64% e.e. for 4e, 17% e.e. for 4f. Catalyst 1a having 3-hydroxypropyl substituent resulted in 81% e.e. for compound 4g. The formation of the (+)-(S)-enantiomer of 4 was preferred using crown ethers 1a–c, while the (−)-(R)-enantiomer was in excess with catalyst 2. The absolute configuration of the Michael adduct 4d was determined by single-crystal X-ray analysis.

Synthesis, extraction ability and application in asymmetric synthesis of azacrown ethers derived from D-glucose

New chiral monoaza-15-crown-5 ethers have been synthesised from 1,2:5,6-di-O-isopropylidene-D-mannitol. The substituent at the nitrogen atom has a major influence on the cation extraction ability of the azacrown. These sugar-based crown ethers show asymmetric induction as chiral phase transfer catalysts in the Michael addition of 2-nitropropane to chalcone (67% ee).

Asymmetric Michael addition and deracemization of enolate by chiral crown ether

Abstract Crown ethers anellated to glucose units have been used to catalyse the enantioselective Michael addition of methyl phenylacetate to methyl acrylate in high chemical yields in up to 84% enantiomeric excess. A novel CH-acid deracemization has also been discovered and the mechanistic rationale of the asymmetric induction is discussed. The proposed mechanism of the addition was also substantiated by molecular mechanics calculations.

Synthesis of chiral 1,3-calix[4](crown-6) ethers as potential mediators for asymmetric recognition processes

Abstract Novel chromogenic 1,3-calix[4](crown-6) derivatives comprised of 1,1′-binaphthyl-, methyl-α- d -glucoside-and d -mannitol moieties in the crown ether ring have been synthesized. UV–vis spectroscopic measurements of the 2,4-dinitrophenylazo chromogenic molecules indicated noticeable chiral discrimination associated with coloration towards primary amine enantiomers.

Novel monoaza- and diazacrown ethers incorporating sugar units and their extraction ability towards picrate salts

A number of new 15- and 1 8-membered ring aza-crown (4, 5, 8–13, 17, 18) and lariat ethers (6, 7) incorporating glucose or galactose units have been synthesized in good yields by a simple route. Their extracting abilities were measured with Li+, Na+, K+ and NH4+ cations. The substituents at the nitrogen atom and the type of monosaccharide affected this property significantly.

Intramolecular ortho and meta photocycloadditions of 4-phenoxybut-1-enes substituted in the arene residue with carbomethoxy, carbomethoxymethyl, and 2-carbomethoxyethyl groups

Abstract On irradiation of 4-phenoxybut-1-enes substituted with a carbomethoxy group in the arene, only the ortho compound 1 led to notable ortho photocycloaddition, while the meta regioisomer 2 furnished meta and ortho photocycloadducts albeit in low yield, and the para -substituted compound 3 resulted only in intractable polymers. On irradiation of the carboxymethyl- and 2-carboxyethyl homologues 4 – 9 , the photoreactivity altered dramatically. The highest yields of meta photocycloadducts were observed on irradiation of the ortho -substituted compounds 4 and 7 . Due to steric hindrance, only one of the two possible regioisomers 18 and 19 , respectively, was formed. The meta -substituted compounds 5 and 8 gave significant amounts of meta photocycloadducts as mixtures of regioisomers 13 + 16 and 14 + 17 , respectively. The intramolecular meta photocycloaddition was directed exclusively to the 2′,6′-positions of the arene and only 1,5-bridged dihydrosemibullvalenes were formed. On irradiation of the ortho - and para -substituted compounds 4 and 7 , and 6 and 9 , respectively, considerable amounts of reaction products derived from initial ortho photocycloaddition were detected.