Dedicated to the memory of late Prof. Dr. Hans Schmid (16. I. 78)
SummaryThe stereochemistry of frans-and cis-2,4-dimethyl-tetrahydroquinolines, 6 and 7 were derived from 'H-NMR. studies. These were converted respectively into transand cis-5,6-dihydro-4,6-dimethyl-4H, 8 H-pyrido [3,2,1-de]phenanthridin-8-ones 18 and 20 by a Pschorr reaction on the anthranilamides 10 and 15. Bromophenanthridones 19 and 21 were similarly prepared from bromoanthranilamides 12 and 17. Detailed 'H-NMR. studies on 18 and 20 indicated axial disposition of the methyl groups at C(2) in both compounds in contrast to the situation in 6 and 7. This is presumably to avoid adverse CH,CO group interaction of the A (1,3) type. The severity of this is gauged by the preference of 20 for a normally forbidding 1,3-diaxial orientation of two methyl groups. X-ray crystallographic studies on 19 and 20 confirm the stereochemical assignments.In an earlier paper [ 11 of this series, we had shown that restricted rotation of the amide bond in cyclic amides having partial structures 1 leads to allylic strain of the A(1-3) type [2] [3], resulting in the group R occupying preferentially the axial position when present on a piperidine ring. NMR. and X-ray crystallographic evidence were adduced to demonstrate this in the case of N-benzoyltetrahydroquinaldine 2 [4], pyridobenzoxazepinone 3 [5], pyridobenzoxazinone 4 [6] and pyridophenanthridone 5 [7]. In these molecules the methyl group had the axial conformation whereas it was equatorially placed in the tetrahydroquinaldine precursors. The study revealed additionally that in 2 and 3 with some measure of I )