Chiral Ligands Derived fromAbrine8. An Experimental and Theoretical Study of Free Ligand Conformational Preferences and the Addition of Diethylzinc to Benzaldehyde

Abstract

Three structurally similar series of 1,2,3,4-tetrahydro-beta-carboline ligands, 4a-d, 6a-d and 7a-d, and two series of chiral oxazolidines, 8a-d and 9a-g, were synthesized and used as chiral catalysts in the addition of diethylzinc to benzaldehyde. The enantioselectivities of the resulting 1-phenyl-1-propanol were obtained in each case, and these ee values were, in most cases, related to the conformational populations of the free ligand as expressed by the calculated differences in the energies of the ligand conformations formed by inversion at nitrogen. This suggested the possible existence of a linear free energy relationship. The effect on enantioselectivity of the carbon chain length of the R group located (1) on the C-3 substituent of 4a-d, 6a-d, and 7a-d or (2) at C-5 in 8a-d and 9a-g was studied in detail. On the basis of the correlations observed and the ligands' structural characterization, a structure was proposed for the transition state during ethyl group transfer when using ligands 8a-d. Furthermore, the change in enantioselectivity was successfully predicted when diastereomeric ligands 11 and 12 were compared in this chiral addition.

Antioxydant activity of β-carboline derivatives in the LDL oxidation model

“…Compound 4a or 4b was engaged in a PicteteSpengler reaction [40] in CH 2 Cl 2 , with TFA and the desired benzaldehyde to afford b-carboline derivatives 5aej,m. Debenzylation reaction of derivatives 5i,j in methanol with Pd/C under hydrogen atmospheric pressure, afforded derivatives 5k,l.…”

Aliphatic aldehydes in the synthesis of carbo- and heterocycles. Part I. Synthesis of three-, four-, and five-membered rings

“…It should be noted that the charge on the C 2 atom originating from the carbonyl group changes to the opposite in going to dithio acetals 117, so that it can be alkylated through lithium derivative 118. This reaction opens the way for conversion of aldehydes into ketones 119 that are difficult to obtain by other methods [144][145][146][147] Chiral 1,3-oxazolidines derived from β-amino alcohols and aldehydes are important intermediates in numerous asymmetric syntheses [148][149][150][151][152][153][154][155][156][157]. Badiang and Aube [158] were the first to develop a procedure for the synthesis of 2-alkyl-4,5-dihydrooxazoles 120 from aldehydes 9d and 9e and β-hydroxyalkyl azides 121.…”

Antioxidant activity of benzoxazolinonic and benzothiazolinonic derivatives in the LDL oxidation model

“…Classical Bischler-Napieralski cyclization afforded, in the presence of phosphorous oxychloride, compounds 10a-c, which were reduced in methanol by sodium borohydride to give derivatives 11a-c. Attempts using Pictet-Spengler reaction 30 in CH 2 Cl 2 with TFA, compound 5a or 5b, and the desired benzaldehyde, to furnish compounds 11a-c were unsuccessful. Alkylation of compounds 11a-c by n-propyl or n-nonyl iodide, in acetonitrile with potassium carbonate, provided the corresponding tertiary amines (12a-d).…”