Chiroptical and conformational properties of (R)-1-phenylethylamine derivatives of persubstituted benzene

Chiral derivatives of 2,4,5,6-tetrachloro-1,3-dicyanobenzene 1 with one, tw o and three (R)-1 -phenylethylamino ((R)-PEA) units 2-4 are prepared and th eir chiroptical and conformational properties discussed on the bases of the UV/CD, NMR and MM2 data. High polarity of the persubstituted benzene ring leads to peculiar UV and IR spectra of achiral model compounds 5-7, whereas relatively rigid conformations of the chiral analogues 2-4 are reflected i n the CD spectra. Strong exciton coupling (EC) appears in the CD spectrum o f pseudo-C-3-symmetric 4; this type of interaction seems not to be present in the C-1-symmetric 2 and C-2-symmetric 3. The absence of a molecular clef t in the chiral structures 2-4 could explain their inability to recognise t he enantiomers of some racemates in the NMR experiment. (C) 1999 Elsevier S cience Ltd. All rights reserved.