已经研究了将三氯甲硅烷基烯酸酯催化,对映选择性加成到醛的机理。使用ReactIR和快速注入NMR(RINMR)光谱进行的动力学研究已证实,涉及一个或两个与硅离子组织中心结合的磷酰胺的双机理途径的同时运行。最初基于催化剂负载量研究和非线性效应研究假定了这种机械二分法。这种二元性解释了各种类型的磷酰胺的反应性和立体选择性的差异。Arrhenius激活参数的确定表明,醛醇的添加是通过可逆的方式发生的,尽管不利的是形成了活化的复合物,并且自然丰度1313 C NMR动力学同位素效应(KIE)研究已经确定,周转限制步骤是添加羟醛。对一系列磷酰胺的彻底检查已经建立了经验结构-活性选择性关系。此外,已经研究了催化剂负载量,添加速率,溶剂和添加剂的影响,这些影响共同形成了醇醛添加的统一机理图。
A total synthesis of (+)-papulacandin D has been achieved in 31 steps, in a 9.2% overall yield from commercially available materials. The synthetic strategy divided the molecule into two nearly equal sized subunits, the spirocyclic C-arylglycopyranoside and the polyunsaturated fatty acid side-chain. The C-arylglycopyranoside was prepared in 11 steps in a 30% overall yield from triacetoxyglucal. The fatty acid side-chain was also prepared in 11 steps in a 30% overall yield from geraniol. The key strategic transformations in the synthesis are: (1) a palladium-catalyzed, organosilanolate-based cross-coupling reaction of a dimethylglucal-silanol with an electron-rich and sterically hindered aromatic iodide and (2) a Lewis-base catalyzed, enantioselective allylation reaction of a dienal and allyltrichlorosilane. A critical element in the successful execution of the synthesis was the development of a suitable protecting group strategy that satisfied a number of stringent criteria. (C) 2010 Elsevier Ltd. All rights reserved.
Synthesis of Phosphoramides for the Lewis Base-Catalyzed Allylation and Aldol Addition Reactions
作者:Scott E. Denmark、Xiping Su、Yutaka Nishigaichi、Diane M. Coe、Ken-Tsung Wong、Stephen B. D. Winter、Jun Young Choi
DOI:10.1021/jo9820723
日期:1999.3.1
Both chiral and achiral phosphoramides of diverse structure were prepared from diamines by the coupling to phosphorus(V) or phosphorus(III) reagents. Several enantiopure 1,2-diphenyl-1,2-ethanediamine analogues have been prepared by the reductive coupling of the corresponding N-silylimine with NbCl(4)(THF)(2) and subsequent resolution by the formation of diastereomeric menthyl carbamates. (S,S)-N,