Catalytic intramolecular hydroamination of aminoallenes using titanium and tantalum complexes of sterically encumbered chiral sulfonamides
Catalytic intramolecular hydroamination of aminoallenes using titanium and tantalum complexes of sterically encumbered chiral sulfonamides
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使用空间阻碍的手性磺酰胺的钛和钽配合物催化氨基丙二烯的分子内氢胺化
DOI：
10.1039/d0dt02557g
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发表时间：
2020
影响因子：
4
通讯作者：
Johnson, Adam
中科院分区：
文献类型：
--
作者：
Sha, Fanrui;Shimizu, Emily A.;Slocumb, Hannah S.;Towell, Sydney E.;Zhen, Yi;Porter, Hanna Z.;Takase, Michael;Johnson, Adam
由于贵金属催化剂的相对稀缺和昂贵，使用地球上丰富的金属的催化是一个重要的目标。使用富含地球的催化剂来合成常见的药物结构基序如吡咯烷和吡啶将是甚至更有益的。因此，开发用于不对称闭环氢胺化的钛催化剂是一个有价值的目标。本工作合成了四种天然氨基酸衍生的空间位阻手性磺胺类化合物。这些化合物与Ti（NMe 2）4或Ta（NMe 2）5发生质子分解反应，得到单体配合物，如DOSY NMR和X射线晶体学所确定的。所得配合物对七-4，5-二烯胺的闭环氢胺化反应具有活性，得到四氢吡啶和吡咯烷产物的混合物。然而，钛络合物将6-甲基庚-4，5-二烯基胺仅转化为2-（2-甲基丙烯基）吡咯烷，对映体选择性高于先前报道的那些，对映体过量范围为18- 24%。相应的钽配合物具有更高的选择性，对映体过量范围为33- 39%。
Catalysis using earth abundant metals is an important goal due to the relative scarcity and expense of precious metal catalysts. It would be even more beneficial to use earth abundant catalysts for the synthesis of common pharmaceutical structural motifs such as pyrrolidine and pyridine. Thus, developing titanium catalysts for asymmetric ring closing hydroamination is a valuable goal. In this work, four sterically encumbered chiral sulfonamides derived from naturally occurring amino acids were prepared. These compounds undergo protonolysis reactions with Ti(NMe2)4 or Ta(NMe2)5 to give monomeric complexes as determined by both DOSY NMR and X-ray crystallography. The resulting complexes are active for the ring closing hydroamination hepta-4,5-dienylamine to give a mixture of tetrahydropyridine and pyrrolidine products. However, the titanium complexes convert 6-methylhepta-4,5-dienylamine exclusively to 2-(2-methylpropenyl)pyrrolidine in higher enantioselectivity than those previously reported, with enantiomeric excesses ranging from 18–24%. The corresponding tantalum complexes were more selective with enantiomeric excesses ranging from 33–39%.