Enzymatic Synthesis of Optically Active a-Hydroxybenzylpyridines
摘要:
Synthesis of optically active alpha-hydroxybenzylpyridines by asymmetric reduction of benzoylpyridines and benzoylpyridine N-oxides with baker's yeast, and enantioselective esterification of racemic alpha-hydroxybenzylpyridines by use of lipase PS have been described.
铬(II)水溶液Cr aq 2+与苯甲酰吡啶氧化物(BPO)的反应比与先前探索的其他吡啶N-氧化物的反应要快得多。在伪一级反应条件下用过量的任何一种试剂研究了动力学。在这两种条件下,主要动力学项均表现出对限制试剂的一阶依赖性,以及对过量试剂的二阶依赖性,即k Cr = k 2 Cr [BPO] [Cr aq 2+ ] 2(过量的Cr aq 2+)并且k BPO = k 2 BPO[Cr aq 2+ ] [BPO] 2(过量BPO),其中k 2 Cr =(6.90±0.27)×10 4 M -2 s -1和k 2 BPO =(3.32±0.28)×10 5 M -2 s -1在0.10 M HClO 4中。速率常数k 2 Cr包含与[H + ]独立和[H + ]催化的路径相对应的项。在提出的机制中,最初形成的Cr aq(BPO)2+参与Cr aq的平行氧化2+和降低BPO。后一反应为Cr(
Iodo- or 2-bromopyridine N-oxides were readily magnesiated with i-PrMgCl·LiCl via the iodine or bromine−magnesium exchange. The bromine adjacent to pyridineN-oxide (at the 2- or 6-position) can be regioselectively magnesiated in the presence of other position substituted halogens. This method was tested in various substituted pyridineN-oxide systems, and has been successfully applied to the total