Kazushi Mashima 교수

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCationic BINAP-Ru(II) Halide Complexes: Highly Efficient Catalysts for Stereoselective Asymmetric Hydrogenation of .alpha.- and .beta.-Functionalized KetonesKazushi Mashima, Koh-hei Kusano, Naomasa Sato, Yoh-ichi Matsumura, Kyoko Nozaki, Hidenori Kumobayashi, Noboru Sayo, Yoji Hori, Takero Ishizaki, and Cite this: J. Org. Chem. 1994, 59, 11, 3064–3076Publication Date (Print):June 1, 1994Publication History Published online1 May 2002Published inissue 1

Abstract The rhodium and iridium (η5-C5Me5)MCl complexes (3a: M = Rh; 3b: M = Ir) of (1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine were found to be catalyst precursors for asymmetric transfer hydrogenation of acetophenone, 2-acetonaphthone, 1-tetralone, and 1-indanone to give (S)-1-phenylethanol (90% ee), (S)-1-(2-naphthyl)ethanol (85% ee), (S)-1-tetralol (97% ee), and (S)-indanol (99% ee), respectively.

Reaction of [RuX2(arene)]2(1) and (S)-BINAP gives cationic BINAP–ruthenium complexes of the formula {RuX(arene)[(S)-binap]} Y (2)(X = Cl, Br, and l; Y = Cl, Br, l, BF4, and BPh4; arene = C6H6 and p-MeC6H4CHMe2) which are efficient catalyst precursors for enantioselective hydrogenation of various prochiral alkenic and ketonic substrates [BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl]; a crystal structure of (2)(with X = Cl, Y = BF4) was obtained.

The salt makes the difference: In the presence of a chiral iridium catalyst, 1- and 3-substituted as well as 1,3-disubstituted isoquinolinium salts can be hydrogenated, giving the corresponding 1,2,3,4-tetrahydroisoquinolines in high enantiomeric excess after a basic workup (see scheme). This protocol is applicable to the synthesis of the prescription drug solifenacin.

Asymmetric allylic alkylation of β-ketoesters with allylic alcohols catalyzed by [Ni(cod)2]/(S)-H8-BINAP was found to be a superior synthetic protocol for constructing quaternary chiral centers at the α-position of β-ketoesters. The reaction proceeded in high yield and with high enantioselectivity using various β-ketoesters and allylic alcohols, without any additional activators. The versatility of this methodology for accessing useful and enantioenriched products was demonstrated.

A new family of heterometallic catalysts based on trimetalated macrocyclic tris(salen) ligands and rare-earth metals was prepared and structurally characterized. The LaZn₃ system containing anionic ligands such as acetate plays a critical role in catalyzing the alternating copolymerization of cyclohexene oxide (CHO) and CO₂ with a high proportion of carbonate linkages. Among the lanthanide metals, the CeZn₃ system exhibits high catalytic activity with a turnover

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLiving Polymerization of Ethylene Catalyzed by Diene Complexes of Niobium and Tantalum, M(.eta.5-C5Me5)(.eta.4-diene)X2 and M(.eta.5-C5Me5)(.eta.4-diene)2 (M = Nb and Ta), in the Presence of MethylaluminoxaneKazushi Mashima, Shinjiro Fujikawa, Yoshiyuki Tanaka, Hisao Urata, Toshiyuki Oshiki, Eiji Tanaka, and Akira NakamuraCite this: Organometallics 1995, 14, 6, 2633–2640Publication Date (Print):June 1, 1995Publication History Published online1 May 2002

An efficient catalytic system of a zinc cluster and tetrabutylammonium iodide (TBAI) was developed for cyclic carbonate synthesis from epoxides and carbon dioxide (CO2) without the use of any organic solvents under very mild conditions (25 °C, 1 atm), even in the presence of impurities such as water and air. Electrophilicity of the central Zn(II) ion, the number of trifluoromethyl groups, nucleophilicity and leaving ability of the anion of alkylammonium salts, and various reaction parameters hav

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPolymerization of ethylene catalyzed by a tantalum system Ta(.eta.3-C5Me5) (.eta.4-diene)(CH3)2/MAO: an isoelectronic analog for group 4 metallocene catalyst (MAO = methylaluminoxane)Kazushi Mashima, Shinjiro Fujikawa, and Akira NakamuraCite this: J. Am. Chem. Soc. 1993, 115, 23, 10990–10991Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://pubs.acs.org/doi/10.1021/ja00076a067

The tetranuclear zinc cluster Zn4(OCOCF3)6O catalyzes the direct conversion of esters, lactones, and carboxylic acids to oxazolines with remarkable chemoselectivity.

Abstract A highly efficient and general iridium‐difluorphos‐catalyzed asymmetric hydrogenation of diverse 2‐alkyl‐ and 2‐aryl‐substituted quinoxalines into biologically and pharmaceutically relevant 2‐substituted‐1,2,3,4‐tetrahydroquinoxaline units has been developed. High isolated yields and excellent enantioselectivities of up to 95% for 2‐alkyl‐substituted quinoxalines and of up to 94% for 2‐aryl‐substituted quinoxalines were obtained.

Highly diastereoselective hydrogenation of methyl 2-benzamidomethyl-3-oxobutanoate has been accomplished by using [Rul{(R)-binap}(p-cymene)]I and corresponding complexes of derivatives of binap as catalyst, giving methyl (2S,3R)-2-benzamidomethyl-3-hydroxybutanoate, a versatile intermediate for the synthesis of β-lactam antibiotics, in up to 98% diastereoisomeric excess and 99% enantiomeric excess.

Snipping tool: Zn(OTf)2 is an efficient catalyst for selective cleavage of amides bearing a β-hydroxyethyl group on the nitrogen atom. The mechanism involves an N,O-acyl rearrangement and transesterification. This new catalytic system can be applied to sequence-specific peptide bond scission at the amine side of a serine residue. Tf=trifluoromethanesulfonyl.

Abstract We prepared the half-sandwich hydride and 16-electron complexes of rhodium and iridium bearing an anion of (1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine: for the iridium catalyst system, a 16-electron complex 2b and an 18-electron, hydride complex 3b were synthesized, while only a 16-electron complex 2a was detected for the rhodium catalyst.