Diazoketones as precursors in β-lactam synthesis. New insights into the mechanism of the photochemically induced Staudinger reaction
作者:Michael R. Linder、Wolfgang U. Frey、Joachim Podlech
DOI:10.1039/b105748k
日期:2001.10.11
Diazoketones 1â3, derived from suitably protected amino acids (Ala, Val and Tle), have been photochemically rearranged in the presence of imines leading exclusively to trans-arranged 4-aryl- and cinnamoyl-substituted β-lactams 17â33 with up to 84% yield. Selectivities were dependent on the steric demand of the amino acid side-chain ranging from 65 â¶ 35 to 90 â¶ 10. The relative configurations were proved by several X-ray crystal structures and comparison of NMR spectra. Further reactions of the azetidinones at position C-4 have been performed: electron-rich aryl substituents (e.g., 4-methoxyphenyl, furyl and thienyl) could be degraded to carboxylic
acids 34 and 35 which were further transformed to acetoxy derivatives (compounds 36 and 37) in a Kolbe reaction of type II. The cinnamoyl group could be oxidized to the formyl group by ozonolysis (â
38, 39). The mechanism of the photochemically induced β-lactam formation is discussed in detail.
从适当保护的氨基酸(Ala、Val和Tle)衍生出的Diazoketones 1–3,在亚胺的存在下通过光化学重排,专一生成了产率高达84%的trans-排列的4-芳基和肉桂酰取代的β-内酰胺17–33。选择性取决于氨基酸侧链的立体需求,范围从65:35到90:10。相对构型通过多个X射线晶体结构和NMR光谱的比较得到了证实。对氮丙啶酮C-4位的进一步反应已经进行:电子富集的芳基取代基(如4-甲氧基苯基、呋喃基和噻吩基)可以降解为羧酸34和35,这些羧酸进一步通过Kolbe II型反应转化为乙酰氧基衍生物(化合物36和37)。肉桂酰基可以通过臭氧分解氧化为醛基(→38, 39)。光化学诱导的β-内酰胺形成机制被详细讨论。