Abstract
The title compounds diacylaminoquinazolinones (DAQs) are enantioselective acylation agents for amines and a detailed study of their stereostructures was undertaken with the aim of understanding how this enantioselectivity arises. The N-N bond in these DAQs is a chiral axis. Even where both
N
-acyl groups are (
S
)-2-acetoxypropanoyl, the N-N bond is still a chiral axis because in the most stable conformation of the planar imide moiety, one
exo
/
endo
orientation of the carbonyl groups is much preferred over the alternative (
endo
/
exo
) as revealed by NMR spectroscopy. A conformational preference within the 2-acetoxypropanoyl grouping accounts for the presence of a single
exo
/
endo
conformation in solution for some of these DAQs (see above) but an interconverting
exo
/
endo
endo
/
exo
mixture for others. Where a single
exo
/
endo
conformation is present in solution, evidence is presented that this closely resembles the X-ray determined crystal structure. A mechanism for the second acylation step to form these DAQs is proposed, which involves preliminary
O
-acylation of the 3-(monoacylamino)quinazolinone.