Catalytic Enantioselective Amination of Enolsilanes Using C₂-Symmetric Copper(II) Complexes as Chiral Lewis Acids

Abstract

[formula: see text] [Cu(S,S)-t-Bu-box](OTf)2 (1) catalyzes the enantioselective amination of enolsilanes with azodicarboxylate derivatives. Isomerically pure enolsilanes of aryl ketones, acylpyrroles, and thioesters added to the azo-imide in greater than 95% ee. The use of an alcohol additive was critical to achieving catalyst turnover.

Development of Atom-Economical Catalytic Asymmetric Reactions under Proton Transfer Conditions: Construction of Tetrasubstituted Stereogenic Centers and Their Application to Therapeutics

“…13,14) Although this specific transformation using azodicarboxylate as a formal "NH 2 ϩ " reagent was discovered in 1954, [15][16][17] its enantioselective variants have only been found recently. [18][19][20][21][22][23] Our particular focus at the beginning of this project in 2006 was the establishment of a concise, practical, and enantioselective synthetic route to Ranirestat (AS-3201, 1), a highly potent aldose reductase inhibitor. [24][25][26] Whereas almost all the other candidate aldose reductase inhibitors were withdrawn during the course of clinical development, 1 was identified as a structurally novel aldose reductase inhibitor bearing a spirosuccinimide entity exhibiting remarkable efficacy and safety.…”

Enantioselective amination of silylketene acetals with (N-arylsulfonylimino)phenyliodinanes catalyzed by chiral dirhodium(II) carboxylates: asymmetric synthesis of phenylglycine derivatives

“…9 Very recently, we demonstrated that the enantioselective amination of silyl enol ethers derived from acyclic ketones or enones with [(2-nitrophenylsulfonyl)imino]phenyliodinane (NsN=IPh, 2b) catalyzed by chiral dirhodium(II) carboxylates provides N-(2-nitrophenylsulfonyl)-α-amino ketones with enantioselectivities of up to 95% ee. 10 In this process, Rh 2 (S-TFPTTL) 4 (1a), 11 characterized by the substitution of fluorine atoms for four hydrogen atoms on the phthalimido group in the parent dirhodium(II) complex, Rh 2 (S-PTTL) 4 (1c), 12 proved to be the catalyst of choice in terms of product yield and enantioselectivity as well as catalytic activity. As a logical extension of our studies, we herein 18 and the catalytic enantioselective hydrogenation of α-aryl imino esters, 19 have been used to synthesize optically active arylglycine derivatives, 20 this protocol provides a new, catalytic asymmetric approach to phenylglycine derivatives.…”

“…On the basis of our previous work, 10 we initially explored the amination of triethylsilylketene acetal 3a (Z:E = 97:3, 1.2 equiv) derived from methyl phenylacetate with NsN=IPh (2b) using 1 mol % of Rh 2 (S-TFPTTL) 4 . The reaction in CH 2 Cl 2 proceeded smoothly at 0 °C to completion in less than 15 min, giving N-(2-nitrophenylsulfonyl)phenylglycine methyl ester (4b) 21 in 95% yield after column chromatography on silica gel ( 21,22 Gratifyingly, switching the catalyst from Rh 2 (S-TFPTTL) 4 to Rh 2 (S-TCPTTL) 4 greatly improved the enantioselectivity, providing 4b in 98% yield with 97% ee (entry 2), although lowering the reaction temperature to -20 °C had little impact on the enantioselectivity (98% ee, entry 3).…”

“…The reaction of silylketene acetals derived from methyl phenylacetates with [N-(2-nitrophenylsulfonyl)imino]phenyliodinane (NsN=IPh) under the catalysis of dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], Rh 2 (S-TCPTTL) 4 , proceeds in benzene at room temperature to give N-(2-nitrophenylsulfonyl)phenylglycine derivatives in high yields and with enantioselectivities of up to 99% ee.---* Corresponding author. Tel.…”

Bisoxazoline (BOX) Ligand-Metal Complexes:An Emerging Chiral Catalyst

“…Several research groups have utilized these bisoxazoline ligands in combination with a wide range of mild Lewis acids as catalysts for carrying out different enantioselective reactions. [4][5][6][7][8][9][10][11][12][13] Recently, chiral BOX-metal(II) complexes covalently anchored to silica and mesoporous MCM-41 have been used as a new heterogenous catalyst for enantioselective Friedel-Crafts hydroxylation.…”