Reaction of the β-lactam-based oxazolidinone 5 with N-sulfonylimines provides the exo and endo azapenams 8 in 22â54% yield. The reactivity of 2H-azirines as 1,3-dipolarophiles towards β-lactam-based azomethine ylides derived from oxazolidinones 5 and 15 has also been evaluated. Azirines 11 and 12a provide cycloadducts 13a,b and 16 respectively, which incorporate the novel 2,6-diazatricyclo[4.2.0.02,4]octan-7-one ring system. These adducts were resistant towards CâN cleavage as the basis of an entry to 1-azacephams (1,5-diazabicyclo[4.2.0]octan-8-ones) 4. The use of the 3-(4-methoxyphenyl)-2H-azirine 19 provides a labile initial cycloadduct, which undergoes in situ ring-cleavage and further reaction to give the 2 â¶ 1 adduct 1-azacepham 22. The initial product is stable when 3-(4-nitrophenyl)-2H-azirine 23 is employed, and cycloadducts 24a and 24b are converted under mild reducing conditions to the 1-azacepham derivatives 25 and 26.
β-内酰胺基
恶唑啉酮5与N-磺
酰亚胺反应生成外环和内环氮杂佩兰8,产率为22-54%。还评估了2H-
氮杂环丙烷作为1,3-偶极亲偶极体与源自
恶唑啉酮5和15的β-内酰胺基
亚胺叶立德的反应活性。
氮杂环丙烷11和12a分别生成含新型2,6-二氮杂
三环[4.2.0.02,4]
辛烷-7-酮环系的环加成物13a,b和16。这些加成物对C-N键断裂具有抗性,从而为获得1-氮杂头孢烷(1,5-二氮杂
双环[4.2.0]辛烷-8-酮)4提供了途径。使用3-(4-甲氧苯基)-2H-
氮杂环丙烷19得到了一个不稳定的初始环加成物,它通过原位环断裂和进一步反应生成2∶1加成物1-氮杂头孢烷22。当使用3-(4-
硝基苯基)-2H-
氮杂环丙烷23时,初始产物是稳定的,并且环加成物24a和24b在温和还原条件下转化为1-氮杂头孢烷衍
生物25和26。