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.
标题化合物二酰
氨基
喹唑啉酮(
DAQs)是针对胺的选择性酰化试剂,针对其立体结构进行了详细研究,以期理解这种对映选择性的来源。这些
DAQs中的N-N键是一个手性轴。即使两个N-酰基团都是(S)-2-
乙酸基丙酰基,N-N键仍然是一个手性轴,因为在平面
亚胺部分的最稳定构象中,一种外-内构象的羰基基团比另一种内-外构象更为优先,NMR光谱学揭示了这一点。2-
乙酸基丙酰基团内的构象偏好解释了某些
DAQs在溶液中存在单一外-内构象(如上所示),而其他则存在互变的外-内⇌内-外混合物。在溶液中存在单一外-内构象的情况下,提供了证据表明,这种构象与X射线确定的晶体结构非常相似。提出了一种形成这些
DAQs的第二步酰化机制,该机制涉及对3-(单酰
氨基)
喹唑啉酮的初步O-酰化。