1969 Volume 42 Issue 10 Pages 2885-2894
The proposed structures of the dimeric products obtained from aliphatic aldehydes and arylamines were reexamined by IR and NMR spectra. The 1,2,3,4-tetrahydroquinoline structure was ascertained in the case of acetaldehyde or propionaldehyde, and aldolic structure was confirmed in the case of n-butyraldehyde. It was observed that the latter readily isomerizes to the former type in the presence of acetic acid. Conformational analysis of a racemic pair of the former (IIIa–c: 2,4-disubstituted, IIId- 2,3,4-trisubstituted) indicated that two isomers of IIIa–c (one has 2-equatorial, 4-quasi-equatorial and the other 2-equatorial, 4-quasi-axial substituents) have a flattened half-chair conformation and two isomers of Hid (one has 2,3-diequatorial, 4-quasi-equatorial, and the other 2-equatorial, 3-axial, 4-quasi-axial substituents) have a more remarkably flattened half-chair, i. e. a nearly plane structure. The acylation of ring nitrogen enhanced this tendency, and one of the 1-acetyl derivatives of III was deduced to have a twist half-boat conformation.
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