Ryo Shintani

Sodium Tetraarylborates as Effective Nucleophiles in Rhodium/Diene-Catalyzed 1,4-Addition to β,β-Disubstituted α,β-Unsaturated Ketones: Catalytic Asymmetric Construction of Quaternary Carbon Stereocenters

A rhodium-catalyzed 1,4-addition of sodium tetraarylborates to beta,beta-disubstituted alpha,beta-unsaturated ketones is described. Highly efficient asymmetric catalysis has also been achieved by employing a readily available chiral diene ligand, leading to the construction of quaternary carbon stereocenters with high enantioselectivity.

Palladium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles via enantioselective C-H bond functionalization.

A Pd-catalyzed asymmetric synthesis of Si-stereogenic dibenzosiloles is developed through enantioselective C-H bond functionalization of prochiral 2-(arylsilyl)aryl triflates. High chemo- and enantioselectivities are achieved by employing a Josiphos-type ligand under mild conditions.

Rhodium-Catalyzed Asymmetric Arylation of N-Tosyl Ketimines

A rhodium-catalyzed addition of sodium tetraarylborates to N-tosyl ketimines is described. Highly efficient asymmetric catalysis has been achieved by employing a chiral diene ligand, constructing chiral amine derivatives possessing α-tetrasubstituted carbon stereocenters with high enantioselectivity.

Stereoselective synthesis of spirooxindoles by palladium-catalyzed decarboxylative cyclization of gamma-methylidene-delta-valerolactones with isatins.

A new synthetic method of spirooxindole derivatives has been developed by way of a palladium-catalyzed decarboxylative cyclization of gamma-methylidene-delta-valerolactones with isatins. By employing a newly prepared phosphoramidite ligand, the reaction proceeds smoothly with excellent diastereoselectivity. Preliminary results of its application to asymmetric catalysis using a chiral phosphoramidite ligand are also described.

Rhodium-Catalyzed Asymmetric Addition of Potassium Organotrifluoroborates to N-Sulfonyl Ketimines

A rhodium-catalyzed asymmetric addition of readily available potassium organotrifluoroborates to both N-tosyl and N-nosyl ketimines has been developed. High enantioselectivity has been achieved by using a chiral diene ligand, and the nosyl group of the addition products can be easily removed while retaining the enantiomeric purity.

Rhodium‐Catalyzed Asymmetric Synthesis of Spirocarbocycles: Arylboron Reagents as Surrogates of 1,2‐Dimetalloarenes

Enantiopure spirocycles that possess a quaternary spirocarbon stereocenter represent an important class of compounds as they can be found in various useful organic molecules, such as natural products, biologically active compounds, and effective chiral ligands for asymmetric catalysis. Construction of such spirocycles using transitionmetal-catalyzed asymmetric carbon–carbon bond-forming reactions are highly desirable in view of the efficiency of the process. In this context, sequential addition of 1,2-dimetalloarenes to 2-cycloalken-1-ones that are tethered at the 3-position to another electrophilic substituent, such as an alkyne, could rapidly afford spirocarbocycles in a convergent manner, as illustrated in Scheme 1; however, the preparation

Palladium-Catalyzed Enantioselective Desymmetrization of Silacyclobutanes: Construction of Silacycles Possessing a Tetraorganosilicon Stereocenter

A palladium-catalyzed desymmetrization of alkyne-tethered silacyclobutanes to give silacycles possessing a tetraorganosilicon stereocenter has been developed, and high chemo- and enantioselectivities have been achieved by the use of a newly synthesized chiral phosphoramidite ligand.

Highly Enantioselective Desymmetrization of Anhydrides by Carbon Nucleophiles: Reactions of Grignard Reagents in the Presence of (−)‐Sparteine

All airand moisture-sensitive manipulations were carried out under argon with standard Schlenk techniques. THF was distilled from sodium benzophenone ketyl under nitrogen. Toluene was purified by passing through a neutral alumina column under argon. (–)-Sparteine (Aldrich), (1S, 2S)-(+)-N-methylpseudoephedrine (Aldrich), (R)-(+)2,2’-isopropylidenebis(4-phenyl-2-oxazoline) (Aldrich), and (+)-quinidine (Avocado) were used without purification. (1R, 2R)-1,2-Dimethoxy-1,2-diphenylethane was prepared according to a literature procedure.1 Phenylmagnesium chloride (2.0 M in THF; Aldrich), 4-methoxyphenylmagnesium bromide (0.5 M in THF; Aldrich), 4-fluorophenylmagnesium bromide (2.0 M in Et2O;

Rhodium-Catalyzed Asymmetric Addition of Arylboronic Acids to β-Phthaliminoacrylate Esters toward the Synthesis of β-Amino Acids

Rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to beta-phthaliminoacrylate esters took place efficiently to give high yields of beta-aryl-beta-amino acid esters with 96-99% enantioselectivity, which was realized by use of a hydroxorhodium/chiral diene complex.

Rhodium-catalyzed asymmetric [5+2] cycloaddition of alkyne-vinylcyclopropanes.

Transition-metal-catalyzed [5+2] cycloaddition of vinylcyclopropanes with carbon carbon unsaturated bonds is an efficient way of constructing seven-membered carbocycles. Several transition metals such as rhodium, ruthenium, nickel, and iron can catalyze these reactions with alkynes as the reaction partner, and alkenes and allenes can also be employed under rhodium catalysis. Unfortunately, however, the development of asymmetric variants of this useful transformation has not met much success so far. In fact, to the best of our knowledge, only a recent report by Wender addressed this issue, achieving high enantioselectivity for several alkene-tethered vinylcyclopropanes using a cationic Rh/(R)-binap catalyst. For cycloaddition of alkyne–vinylcyclopropanes, in contrast, there is no effective catalytic asymmetric method available to date. Herein we describe the development of such an asymmetric catalysis by the use of a rhodium complex coordinated with chiral phosphoramidite ligand, achieving very high enantiomeric excesses (up to >99.5 % ee). Initially, we employed alkyne–vinylcyclopropane 1 a as a model substrate and attempted a cycloaddition reaction in the presence of 5 mol % of a cationic Rh/(R)-binap complex in dichloromethane at 30 8C (Table 1, entry 1). Under these conditions, 37 % yield of cycloadduct 2 a was obtained after 5 h with moderate ee value of 64 %. The use of other axially chiral bisphosphine ligands such as (R)-segphos and (R)-H8-binap [13] resulted in lower yields and enantioselectivity under otherwise the same conditions (18–29 % yield, 46–55 % ee ; entries 2 and 3). In contrast, chiral phosphoramidite ligand (S,S,S)-3 (1.5 equiv to Rh) induced somewhat better enantioselectivity (75 % ee ; entry 4) and its diastereomeric ligand (S,R,R)-3 dramatically improved both reactivity and stereoselectivity, giving product 2 a in 88 % yield with as high as 99 % ee (entry 5). The absolute configuration of 2 a thus obtained was determined to be (R) by X-ray crystallographic analysis as shown in Figure 1. The scope of the present catalysis using ligand (S,R,R)-3 is illustrated in Table 2. Not only aryl groups (1 a–c) but also alkyl groups (1 d and 1 e) are well tolerated as the substituent on the alkyne, leading to the corresponding cycloadducts 2 with uniformly high yield and excellent enantioselectivity (87–90 % yield, 94 % ee ; entries 1–6), and the amount of ligand (S,R,R)-3 can be reduced to 6 mol % (1.2 equiv to Rh) as shown in entry 2. High enantioselectivity is also achieved with substrate 1 f having a terminal alkyne, although [a] Dr. R. Shintani, H. Nakatsu, K. Takatsu, Prof. Dr. T. Hayashi Department of Chemistry, Graduate School of Science Kyoto University, Sakyo, Kyoto 606-8502 (Japan) Fax: (+81) 75-753-3988 E-mail : shintani@kuchem.kyoto-u.ac.jp thayashi@kuchem.kyoto-u.ac.jp Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200901463. Table 1. Ligand effect in the rhodium-catalyzed asymmetric [5+2] cycloaddition of 1 a.