SmI2-Mediated Cyclizations of Derivatized β-Lactams for the Highly Diastereoselective Construction of Functionalized Prolines
摘要:
A series of C4-keto-functionalized 1-[(benzoyloxy)(ethoxycarbonyl)methyl]-2-azetidinones were prepared and studied for their tendency to undergo a Reformatsky-type cyclization to fused bicyclic or tricyclic beta-lactams with the single-electron reducing agent samarium diiodide. Whereas the azetidinone 21a underwent reductive cyclization, affording the potent antibiotic sanfetrinem's tricyclic [4.5.6] core structure as the major component, all other examples tested resulted in cyclization followed by an N to O acyl migration involving cleavage of the beta-lactam ring as the favored pathway. Highly functionalized proline derivatives were therefore accessed as single diastereomers through the reductive cyclization of benzoates 21b, 22, 23a,b, 24b, and 25-28. Pertinent for the success of these cyclizations was the addition of 1 equiv of tert-butyl alcohol, allowing for the protonation of the basic amide derivative obtained after the acyl migration step. The diastereoselectivities of these reactions deviate from those of similar cyclizations involving the corresponding lithium enolate. This divergence could be rationalized by the coordination of the metal ion of the samarium(III) enolate intermediate to the beta-lactam amide functionality in the cyclization step, which may not be possible for lithium enolates.
Synthesis of esters of the potent anti-bacterial trinems and analogues
作者:P. Mark Jackson、Stanley M. Roberts、Silvia Davalli、Daniele Donati、Carla Marchioro、Alcide Perboni、Stefano Proviera、Tino Rossi
DOI:10.1039/p19960002029
日期:——
Coupling the silylenolether 5 and the β-lactam 9(R = Me3Si) affords the ketones 13a–d. Compounds 13a, 13c and 13d are converted into the tricyclic lactams 16–20, 23–25. (Chemoenzymatic synthesis of optically pure silylenolether 5 gave access to homochiral lactams 23–25.) In addition the ketoazetidinones 13 are protected as the 1,3-oxazanes 30. A hydroxyethyl moiety is introduced into these oxazanes
甲硅烷基烯醇醚5和β-内酰胺9(R = Me 3 Si)偶联得到酮13a-d。化合物13a,13c和13d转化为三环内酰胺16-20、23-25。(光学纯的甲硅烷基烯醇醚5的化学酶法合成可得到同手性内酰胺23-25。)此外,酮氮杂环丁酮13被保护为1,3-恶唑烷30。使用Bouffard方法进行所需的立体化学反应,得到醇32。形成相应的碳酸硝基苄酯,脱保护和氧化提供了酮35a和35b,其随后分别转化为三苯甲基41a和41b。
Concise syntheses of 4-(arylcarbonylmethyl)-azetidin-2-ones and related systems
作者:Anthony G. M. Barrett、Peter Quayle
DOI:10.1039/c39810001076
日期:——
On catalysis by trimethylsilyl trifluoromethane-sulphonate, 4-acetoxy-1-trimethylsilylazetidin-2-one reacted with the enol silanes [R1CHC(OSiMe3)R2] to give the β-lactams [[graphic omitted]HCH(R1)COR2] in excellent yields (71 to 95%).