A new, efficient and highly enantioselective synthesis of methyl p-nitrophenyl alkylphosphonates 4 a-c is described. Alkylphosphonic dichloride 1 a-d reacted successively with L-proline ethyl ester and p-nitrophenol to afford phosphoramidates 3 a-d in 97% de. Boron trifluoride catalysed methanolysis gave 4 a-c with 93% ee. Absolute configurations of compounds 4 c and 3 c were established by correlation with the X-ray structure of HPL-colipase-(-)-4 c complex. 31P NMR studies indicates that monochloro phosphoramidates (R p )- and (S p)-2 c undergo fast epimerisation. The observed diastereoselectivity in favour of (S p)-3 c results from a faster reaction of (R p)-2 c as compared to its epimer, according to the Curtin-Hammett principle.
报道了一种新的、高效且高对映选择性的甲基p-
硝基苯基烷基
膦酸酯4a-c的合成方法。烷基膦二
氯化物1a-d与
L-脯氨酸乙酯和p-
硝基苯酚连续反应,以97%的对映体过量率得到了膦酰胺酯3a-d。在
三氟化硼催化下进行
甲醇分解反应,得到了93%对映体纯度的产物4a-c。通过与HPL-colipase-(-)-4c复合物的X射线结构相关联,确定了化合物4c和3c的绝对构型。31P NMR研究表明,单
氯膦酰胺酯(Rp)-和(Sp)-2c发生了快速差向异构化。根据Curtin-Hammett原理,相比于其差向异构体,(Rp)-2c的反应速度更快,这解释了观察到的(Sp)-3c的立体选择性优势。