Conformational study of some 2, 4-diaryl-7-(t-butyl) –3-azabicyclo [3.3.1] nonan-9-ones. Detection of minor isomer with chair- boat conformation

Abstract

2,4-Diaryl-7-(t-butyl)-3-azabicyclo[3.3.1]nonan-9-ones have been synthesized by the reaction of 4-t-butylcyclohexanone with five different aromatic aldehydes and ammonium acetate. 1H and 13C NMR spectra have been recorded for the products in all the five cases. 1H-1H COSY, NOESY, HSQC and HMBC spectra have been recorded for the product obtained using p-isopropylbenzaldehyde. The NMR spectra suggest that the product contains two isomers. The spectral data suggest that the major isomer is 2r,4c-diaryl-7c-(t-butyl)-3-azabicyclo[3.3.1]nonan-9-one adopting twin-chair conformation with equatorial orientations of the aryl and t-butyl groups. The major isomers are termed as 1, 2, 3, 4 and 5. The minor isomer is 2r,4c,diaryl-7t- (t-butyl)-3-azabicyclo[3.3.1]nonan-9-one adopting chair-boat conformation with equatorial orientations of the aryl groups and t-butyl group in the bowspirit position. The minor isomers are termed as 1′, 2′, 3’, 4’ and 5′. Single crystal has been obtained from the product when aryl is p-methoxyphenyl. X-Ray crystallographic study of this crystal shows that it is the major isomer 3 adopting twin-chair conformation with equatorial orientations of the p-methoxyphenyl and t-butyl groups. The formation of minor isomer suggests that 4-t-butylcyclohexanone exists in boat conformation with the t-butyl group in the bowspirit position to some extent.