Synthesis and ¹H and ¹³C NMR spectral study of some t(3)-aryl-r(2),c(4)- dicarbalkoxy-c(5)- hydroxy-t(5)- methylcyclohexanones and their oximes

Abstract

1004-1013Eight t(3)-aryl-r(2),c(4)-bis(carbalkoxy)-c(5)- hydroxy-t(5)-methylcyclohexanone oximes 4a (Ar = Ph; R = Et), 5a (Ar = p-NO₂C₆H₄; R = Et), 6a (Ar = p-ClC₆H₄; R = Et), 7a (Ar = Ph; R = Me), 8a (Ar = p-NMe₂C₆H₄; R = Me), 9a (Ar = m-NO₂C₆H₄; R = Me), 10a (Ar = p-FC₆H₄; R = Me) and 11a (Ar = p-OMeC₆H₄; R = Me) have been synthesized by treating the corresponding ketones with NH₂OH in the presence of sodium acetate. Ketones 8-11 have been newly synthesized by condensing methyl acetoacetate with the appropriate aromatic aldehyde in presence of methylamine. ¹H and ¹³C NMR spectra of ketones 7, 8, 10 and 11 and oximes 4a, 5a and 6a have been recorded in CDCl₃. ¹H and ¹³C NMR spectra of ketone 9 and the other oximes 7a-11a have been recorded in DMSO-d₆ since they are insoluble in CDCl₃. HOMOCOR spectrum has been recorded for 7 (in CDCl₃) and 7a. NOESY spectrum has been recorded for 4a, 7 (in CDCl₃ and DMSO-d₆), 7a and 8a. HSQC spectrum has been recorded for 7 (in CDCl₃) and 7a. HMBC spectrum has been recorded for 5a and 7a. DEPT spectrum has been recorded for 4a. The observed vicinal coupling constants suggest that all the compounds studied exist largely in chair conformation with axial orientations of the hydroxyl group at C-5 and equatorial orientations of all the other substituents. All the oximes have E configuration about C=N bond. The OH-proton at C-5 prefers to be anti to C(5)-C(6) bond in CDCl₃ but anti to C(4)-C(5) bond in DMSO-d₆. Change of solvent from CDCl₃ to DMSO-d₆ has a marked effect on the chemical shifts of the protons in the cyclohexane ring and OH proton. Among the two methylene protons at C-6 the equatorial proton has a higher chemical shift than the axial proton in CDCl₃ but a reverse trend is observed in DMSO-d₆. However,¹³C chemical shifts are not influenced by the change of solvent. Oximation shields all the ring carbons of the cyclohexane ring except C-4. Oximation shields all the protons in the cyclohexane ring except H-6e, which is deshielded by about 0.9 to 1.0 ppm. Use of ¹H and ¹³C chemical shifts for determining the configuration and conformation of oximes is also discussed