The Development of Scalemic Multidentate Niobium Complexes as Catalysts for the Highly Stereoselective Ring Opening of meso-Epoxides and meso-Aziridines
详细信息 查看全文
- 作者：Kenzo Arai ; Simone Lucarini ; Matthew M. Salter ; Kentaro Ohta ; Yasuhiro Yamashita ; Sh
//pubs.acs.org/images/entities/umacr.gif" border="0"> Kobayashi
- 刊名：Journal of the American Chemical Society
- 出版年：2007
- 出版时间：July 4, 2007
- 年：2007
- 卷：129
- 期：26
- 页码：8103 - 8111
- 全文大小：187K
- 年卷期：v.129,no.26(July 4, 2007)
- ISSN：1520-5126
文摘
The discovery and development of a new Lewis acid system based on a complex formed fromniobium(V) methoxide and (R)-3,3'-bis(2-hydroxy-3-isopropylbenzyl)-1,1'-binaphthalene-2,2'-diol, a noveltetradentate BINOL derivative, is presented. The system was shown to be extremely effective in promotingthe desymmetrative ring opening of linear and cyclic meso-epoxides using anilines as nucelophiles, deliveringthe corresponding (R,R) anti-amino alcohols in good to excellent yields (up to quantitative) and excellentenantioselectivity (up to 96% ee). Furthermore, the catalyst system displays a remarkable sensitivity tosteric bulk at the 
-carbon of the epoxide, selectively facilitating ring opening of smaller epoxides in thepresence of more sterically hindered epoxides. This property was confirmed by a series of competitionreactions using a mixture of meso-2-butene oxide and another aliphatic meso-epoxide, with the result thatthe former, less encumbered epoxide reacted preferentially with up to 98% chemical selectivity. While itwas found to be most convenient to conduct the reactions with 10 mol % catalyst loading at 0.16 M, athigher overall concentration the reaction still proceeded efficiently with as little as 0.25 mol % catalyst togive the desired products with no significant reduction in yields or enantioselectivities. In addition, the currentcatalyst system was also found to mediate the asymmetric ring opening of nonsymmetrical cis-2-alkeneoxides with anilines to give preferentially the corresponding (2R,3R)-2-amino-3-ols arising from ring openingat the methyl terminus, in excellent yields (up to quantitative) and good to excellent regio- andenantioselectivities (up to 18:1 and >99% ee, respectively). Intriguingly, it was discovered that the samecatalyst system also promoted the ring-opening desymmetrization of aziridines with aniline nucleophiles togive the corresponding (S,S) vicinal diamines in good to excellent yields and enantioselectivity (up to 95%and 84% ee [>99% ee following a single recrystallization]). Catalyst systems that promote closely relatedreactions with opposite stereochemical outcomes in high selectivity such as the current niobium systemare extremely unusual. To the best of our knowledge, this report constitutes not only the first example ofthe catalytic desymmetrization of both meso-epoxides and meso-aziridines but also a rare example ofsuch complementary stereoselectivity in a catalytic reaction.
-carbon of the epoxide, selectively facilitating ring opening of smaller epoxides in thepresence of more sterically hindered epoxides. This property was confirmed by a series of competitionreactions using a mixture of meso-2-butene oxide and another aliphatic meso-epoxide, with the result thatthe former, less encumbered epoxide reacted preferentially with up to 98% chemical selectivity. While itwas found to be most convenient to conduct the reactions with 10 mol % catalyst loading at 0.16 M, athigher overall concentration the reaction still proceeded efficiently with as little as 0.25 mol % catalyst togive the desired products with no significant reduction in yields or enantioselectivities. In addition, the currentcatalyst system was also found to mediate the asymmetric ring opening of nonsymmetrical cis-2-alkeneoxides with anilines to give preferentially the corresponding (2R,3R)-2-amino-3-ols arising from ring openingat the methyl terminus, in excellent yields (up to quantitative) and good to excellent regio- andenantioselectivities (up to 18:1 and >99% ee, respectively). Intriguingly, it was discovered that the samecatalyst system also promoted the ring-opening desymmetrization of aziridines with aniline nucleophiles togive the corresponding (S,S) vicinal diamines in good to excellent yields and enantioselectivity (up to 95%and 84% ee [>99% ee following a single recrystallization]). Catalyst systems that promote closely relatedreactions with opposite stereochemical outcomes in high selectivity such as the current niobium systemare extremely unusual. To the best of our knowledge, this report constitutes not only the first example ofthe catalytic desymmetrization of both meso-epoxides and meso-aziridines but also a rare example ofsuch complementary stereoselectivity in a catalytic reaction.