Phase-Transfer-Catalyzed Asymmetric Synthesis of Axially Chiral Anilides
Phase-Transfer-Catalyzed Asymmetric Synthesis of Axially Chiral Anilides
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DOI：
10.1002/asia.201301036
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发表时间：
2013-12-01
影响因子：
4.1
通讯作者：
Maruoka, Keiji
中科院分区：
文献类型：
--
作者：
Liu, Kun;Wu, Xiangfei;Maruoka, Keiji
通过联萘修饰的手性季铵盐催化的N-烷基化反应，在相转移条件下实现了轴向手性邻碘苯胺和邻叔丁基苯胺的催化不对称合成。轴向手性产物的合成效用在各种转化中得到证明。例如，轴向手性N-烯丙基-邻碘苯胺通过自由基环化反应转化为3-甲基吲哚啉，具有从轴向手性到C-中心手性的高手性转移。此外，邻叔丁基苯胺的轴向手性的立体化学信息可以用作模板来控制后续转化的立体化学。以联萘修饰的手性溴化铵和邻碘苯胺为原料合成了苯胺铵，并根据其晶体结构讨论了该相转移反应的过渡态结构。手性四烷基溴化铵作为相转移催化剂，识别苯胺邻位取代基之间的空间位阻差异，获得高的对映选择性。研究了苯胺邻位取代基的大小和结构对手性苯胺的影响，合成了具有多种功能基团的轴向手性苯胺，并具有较高的对映选择性。该方法是迄今为止报道的以高度对映选择性的方式获得各种轴向手性苯胺的唯一通用方法。
Catalytic asymmetric synthesis of axially chiral o-iodoanilides and o-tert-butylanilides as useful chiral building blocks was achieved by means of binaphthyl-modified chiral quaternary ammonium-salt-catalyzed N-alkylations under phase-transfer conditions. The synthetic utility of axially chiral products was demonstrated in various transformations. For example, axially chiral N-allyl-o-iodoanilide was transformed to 3-methylindoline by means of radical cyclization with high chirality transfer from axial chirality to C-centered chirality. Furthermore, stereochemical information on axial chirality in o-tert-butylanilides could be used as a template to control the stereochemistry of subsequent transformations. The transition-state structure of the present phase-transfer reaction was discussed on the basis of the X-ray crystal structure of ammonium anilide, which was prepared from binaphthyl-modified chiral ammonium bromide and o-iodoanilide. The chiral tetraalkylammonium bromide as a phase-transfer catalyst recognized the steric difference between the ortho substituents on anilide to obtain high enantioselectivity. The size and structural effects of the ortho substituents on anilide were investigated, and a wide variety of axially chiral anilides that possess various functional groups could be synthesized with high enantioselectivities. This method is the only general way to access a variety of axially chiral anilides in a highly enantioselective fashion reported to date.