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

Abstract

Abstract-The first catalytic enantioselective amination of silylketene acetals with (N-arylsulfonylimino)phenyliodinanes is described. 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.: +81-117-063-236; fax: +81-117-064-981; e-mail: hsmt@pharm.hokudai.ac.jp.The catalytic asymmetric amination of silylketene acetals is one of the most straightforward methods for the preparation of enantioenriched α-amino esters.1,2 In 1999, Evans and Johnson described the first catalytic enantioselective amination of thioester silylketene acetals or silylketene aminals of acylpyrroles with azodicarboxylate derivatives, in which enantioselectivities up to 99% ee were achieved with the use of a Cu(OTf) 2 -bis(oxazoline) catalyst. 3,4Kobayashi and co-workers later reported that a AgClO 4 -BINAP system catalyzed the amination of the silylketene acetal of phenyl propionate with dibenzyl azodicarboxylate with good enantioselectivity (51% ee). 5 In this context, the aziridination of silylketene acetals followed by ring opening of the aziridine intermediate provides a prototypical approach to catalytic asymmetric synthesis of α-amino esters. 6 In 1994, Evans and co-workers reported the first copper(I)-catalyzed amination of silylketene acetals using [(p-tolylsulfonyl)imino]phenyliodinane (TsN=IPh, 2a) as a nitrene precursor, 7 and they concluded that this protocol does not represent a practical approach to the synthesis of α-amino esters. While high levels of enantiocontrol in aziridinations of alkenes have already been achieved using a variety of different chiral transition metal-catalysts, 8 the catalytic enantioselective amination reaction of silylketene acetals with (Narylsulfonylimino)phenyliodinanes has, to the best of our knowledge, not been reported. 9Very 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.

Synthesis of Hypervalent Iodine(III) Reagents Containing a Transferable (Diarylmethylene)amino Group and Their Use in the Oxidative Amination of Silyl Ketene Acetals

“…Direct oxidative α‐amination of carbonyl compounds in the carboxylic acid oxidation state is one of the most straightforward methods for preparing unnatural α‐amino acid derivatives, which are promising structural motifs for the preparation of biologically active molecules. In addition to direct methods, oxidative amination of silyl ketene acetals is also a practical and reliable strategy, and several transition‐metal‐catalyzed approaches have been reported to date, in which iminoiodanes, hydroxyamines, and chloramines were used as a nitrogen source. However, a remaining issue is the need for transition‐metal catalysts and difficulties associated with the further elaboration of the amino group in the products.…”

Hypervalent iodine reagents in the total synthesis of natural products

“…123 The enantioselective amination of silyl enol ethers using a chiral rhodium(II) catalyst has 52 been developed 357 and applied in the formal total synthesis of (─)-metazocine 358 and in the synthesis of (─)-ritodrine 359 by Hashimoto and co-workers.…”

Continuous Flow System with a Polymer‐Supported Dirhodium(II) Catalyst: Application to Enantioselective Carbonyl Ylide Cycloaddition Reactions

“…, [25][26][27] the chlorinated analogue of 1 a, is an exceptionally effective catalyst for enantioselective tandem carbonyl ylide formation-1,3-dipolar cycloaddition reactions of 2-diazo-3,6-diketoesters with arylacetylene, alkoxyacetylene, and styrene dipolarophiles, in which high levels of asymmetric induction (up to 99 % ee) as well as perfect exo diastereoselectivity for styrenes were achieved.…”

“…[24] Given that the com- plex 6 was a remarkably effective catalyst for intramolecular C À H insertion reactions, we were intrigued by the applicability of a polymer-supported dirhodium(II) complex to intermolecular metal-carbene transformations. We previously reported that [Rh 2 A C H T U N G T R E N N U N G (S-TCPTTL) 4 ] (1 b), [25][26][27] the chlorinated analogue of 1 a, is an exceptionally effective catalyst for enantioselective tandem carbonyl ylide formation-1,3-dipolar cycloaddition reactions of 2-diazo-3,6-diketoesters with arylacetylene, alkoxyacetylene, and styrene dipolarophiles, in which high levels of asymmetric induction (up to 99 % ee) as well as perfect exo diastereoselectivity for styrenes were achieved. [26a, 28, 29] Herein, we report the immobilization of a chiral chlorinated dirhodium(II) complex and its use for enantioselective carbonyl ylide cycloaddition reactions under continuous flow conditions.…”