Synthetic Study of Macrocyclic Terpenoids by the Pummerer-type alpha-Allylation of Chiral Selenoxides

A CH_2Cl_2解决方案l-甲基2-苯基硒基乙酸酯（1a）被处理为mCPBA，以相应的硒氧化物2a作为稳定的无色素针。The ^1 H NMR and ^3 CNMR spectra of 2 a indicated that 2 a was obtained as an equilibrated 1 ： 1 mixture at the Se-O bond。在另一方面， mCPBA氧化2-phenylselenylacetate（1b）只将回收的硒氧化物从硒氧化物中还原到常规工作期间。因此，很明显，类固醇保护对硒基功能的稳定性产生了影响。其次，一个CH_2Cl_2解决方案被处理为2a与（CF_3CO）_2O或BF_3·OE_在存在酰三甲基硅烷与可分离的变性体混合物（1<t2>：（1）α-芳香化合物（l-甲基2-苯基硒基-4-戊烯酸（3a））中的硒基1a和二苯醚。2b的一罐α络合物也是通过对1b与mCPBA、丙三甲基硅烷和（CF_3CO）_2O的步骤治疗而产生的。对于类似的α络合物，2b的有机络合物也是有效的，但对crude反应混合物产生了如此差的染色ogaphic纯化。硒氧化物的α-络合2是为了通过Pummer型反应产生硒离子的核药理攻击从2.Furthermore， mCPBA氧化物的代谢混合物中的3a-L-甲基（2 E）-2，4-五戊二酸（4a）通过硒氧化物的热syn elimination。Thus，硒氧化物的南瓜型阿尔法中毒2被描述为一种新型的同源反应，因为它是碳链的一种新的同源反应。

A CH_2Cl_2 solution of l-menthyl 2-phenylselenenylacetates (1a) was treated with mCPBA to give the corresponding selenoxide 2a as stable colorless needles. The ^1H NMR and ^3CNMR spectra of 2a indicated that 2a was obtained as an equilibrated 1 : 1 mixture at the Se-O bond. On the other hand, mCPBA oxidation of the ethyl 2-phenylselenenylacetate (1b) only gave the recoverted selenide due to the deoxygenation from the selenoxide 2b during the usual workup. Thus, it was obvious that the steric protection was effectvie for the stabilization of seleninyl functionality.Subsequently, a CH_2Cl_2 solution of 2a was treated with (CF_3CO)_2O or BF_3・OE_<t2> in the presence of allyltrimethylsilane to affod an inseparable diastereomeric mixture (1 : 1) of the alpha-allylation products (l-menthyl 2-phenylselenenyl-4-pentenoate (3a)) besides selenide 1a and diphenyl diselenide. One-pot alpha-allylation of 2b was also carried out by the stepwise treatment of 1b with mCPBA,allyltrimethylsilane, and (CF_3CO)_2O.The use of the allyltributylstannanes was also effective for the similar alpha-allylation of 2a, but the unavoidable contamination of organostannanes to the crude reaction mixture made the chromatogaphic purification of the products so difficult. The alpha-allylation of selenoxides 2 was thought to proceed through the nucleophilic attack of allylsilane to the selenonium ion generated by the Pummerer type reaction from 2.Furthermore, mCPBA oxidation of the diastereomeric mixture of 3a gave l-menthyl (2E)-2,4-pentadienoate (4a) through thermal syn elimination of selenoxides. Thus, the Pummerer-type alpha-allylation of selenoxides 2 was regarded as being a novel homologation reaction of carbon chains.