Highly enantioselective hydrosilylation of ketones with chiral and C2-symmetrical bis(oxazolinyl)pyridine-rhodium catalysts

Abstract

Chiral and C2-symmetrical 2,6-bis(4'-R-oxazolin-2'-yl)pyridines (pybox, la-e, R = t-Pr, sec-Bu, f-Bu, Et, and Ph) have been newly designed and synthesized from the corresponding optically active d-amino alcohols and pyridine-2,6-dicarboxylic acid as auxiliaries for metal-catalyzed reactions. We have found that the trivalent rhodium-pybox complexes 2a-e can act as catalysts for asymmetric reduction of ketones

Lewis Acid Catalysis of the Diels–Alder Reaction Using Niobium and Tantalum Chlorides in the Presence of Coordinating Ligands

“…The analyses for ip-pybox (1), ib-pybox (2), phen-pybox (3) and benz-pybox (4) were in agreement with literature values [12,13] and the ligands were synthesised in 30-50% overall yield. The Diels-Alder reactions were carried out at −40°C under argon in dichloromethane (DCM) for 24-48 h. MCl x (0.50 mmol) was reacted with ligand (0.55 mmol) in dry DCM under argon.…”

“Pocket Dendrimers” as Nanoscale Receptors for Bimolecular Guest Accommodation

“…49, 126.02, 128.44, 128.63, 128.72, 135.18, 138.17, 154.36, 164.27 ppm; IR (film between KBr discs): ñ = 1728 cm À1 (C=O); MS (FAB): m/z: 348.1 [M+H] + ; elemental analysis calcd (%) for C 21 H 17 NO 4 : C 72. 61, H 4.93, N 4.03; found: C 72.55, H 4.85 55.36, 67.34, 70.13, 99.97, 102.15, 105.23, 107.40, 126.07, 137.45, 138.34, 138.98, 154.27, 160.12, 161.02, 164.19 Synthesis of diamidopyridine-functionalized zinc-porphyrin 6 a: A solution of 2-amino-6-acetamidopyridine (54 mg, 0.36 mmol), [15] [5-(4-car-A C H T U N G T R E N N U N G boxyphenyl) -10,15,20-triphenylporphinato]zinc(II) (130 mg, 0.18 mmol), [7] and bromo-tris(pyrrolidino)phosphonium hexafluorophosphate (PyBroP, 126 mg, 0.27 mmol) as a coupling reagent in dichloromethane (20 mL) was treated with N,N-diisopropylethylamine (DIEA, 0.54 mmol) under stirring at 0 8C. The ice bath was removed after 1 min and the stirring continued at room temperature for 48 h. The reaction mixture was concentrated and the residue dissolved in ethyl acetate.…”

Bioreduction of substituted a-tetralones promoted by Daucus carota root

“…The residue was purified by silica flash chromatography (hexanes:AcOEt, 7:3 as eluent), to give 3b as a colorless oil (0. 6.76 (dd, J 9 Hz and J 3 Hz, 1H), 7.32 (d, J 9 Hz, 1H). The alcohol 3b is unstable and decomposed before fully characterization.…”

“…[1][2][3][4] Therefore, many efforts have been dedicated to search for reactions that can furnish homochiral α-tetralols. There are several reports dealing with the asymmetric hydrogenation of the α-tetralone itself, [5][6][7][8][9][10][11] as well as with its bioreduction, using either isolated enzymes or microorganisms. [12][13][14][15][16] It is of note that substituted homochiral β-tetralols have been obtained by reacting a large variety of enzymes and microorganisms with the corresponding β -tetralones.…”