14447-03-1Relevant articles and documents
The first complete identification of a diastereomeric catalyst-substrate (alkoxide) species in an enantioselective ketone hydrogenation. Mechanistic investigations
Daley, Christopher J. A.,Bergens, Steven H.
, p. 3680 - 3691 (2002)
The enantioselective hydrogenations of the dialkyl 3,3-dimethyloxaloacetate ketone substrates (2, 3, and 4; alkyl = Me, iPr, and tBu, respectively) were catalyzed by [Ru((R)-BINAP)(H)(MeCN)n(sol)3-n]-(BF4) (1, n = 0-3, sol = THF or MeOH, (R)-BINAP = (R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) in up to 82% ee (R). Reaction of the active catalyst 1 with 1 equiv of substrate (2, 3, or 4) in THF or MeOH solution formed the diastereomeric catalyst-alkoxide complexes [Ru((R)-BINAP)(MeCN)(OCH(CO2R)-(C(CH3)2 CO2R))](BF4) (5/6 R = Me, 8/9 R = iPr, and 10 R = tBu, respectively) via hydride addition to the ketone carbonyl carbon and ruthenium addition to oxygen. The absolute configurations at the alkoxide groups ((R)- for the major diastereomers 5, 8, and 10) were determined via cleavage of the ruthenium-alkoxide bond with 1 equiv of HBF4·OEt2. The solution structures of the major diastereomer catalyst-alkoxide complexes (5, 8, and 10) were unambiguously determined by variable-temperature NMR spectroscopy. The major diastereomers (5, 8, and 10) had the same absolute configuration as the major product enantiomers from the catalytic hydrogenation of 2, 3, and 4 with 1 as catalyst. The ratio of major to minor alkoxide diastereomers was similar to the ee of the catalytic hydrogenation. The catalyst-alkoxide complexes are formed at temperatures as low as -30 °C with no other precursors or intermediates observed by NMR showing that ketone-hydride insertion is likely not the turnover limiting step of the catalytic hydrogenation. Results from the stoichiometric hydrogenolysis of 5/6, 8/9, or 10 indicate that their formation is rapid and only partially reversible prior to the irreversible hydrogenolysis of the ruthenium-oxygen bond. The stereoselectivities of the formation and hydrogenolysis of 5/6, 8/9, and 10 sum up to equal the stereoselectivities of the respective catalytic hydrogenations of 2, 3, and 4. The rates of the hydrogenolysis were consistent with these diastereomers being true catalytic intermediates.
Enantioselective catalysis of the intermolecular [2+2] photocycloaddition between 2-pyridones and acetylenedicarboxylates
Maturi, Mark M.,Bach, Thorsten
, p. 7661 - 7664 (2014)
Intermolecular [2+2] photocycloadditions represent the most versatile and widely applicable of photochemical reactions. For the first time, such intermolecular reactions have been carried out in a catalytic fashion using a chiral triplet sensitizer, with high enantioselectivity (up to 92 % ee). The low catalyst loading (2.5-5 mol %) underlines the high efficiency of the process both in terms of reaction acceleration and differentiation of the enantiotopic faces of the substrate. The substrate is anchored to the chiral catalyst through noncovalent interactions (hydrogen bonds), thus providing a chiral environment in which the enantioselective photocycloaddition proceeds. The densely functionalized products present numerous possibilities for further synthetic transformations.
PPh3-catalyzed ring-expansion reactions of sulfamate-derived cyclic imines with acetylenedicarboxylates
Yang, Zhilin,Yu, Hao,Zhang, Lei,Wei, Hang,Xiao, Yumei,Chen, Lanzhen,Guo, Hongchao
supporting information, p. 313 - 318 (2014/01/06)
The PPh3-catalyzed ring-expansion reaction of sulfamate-derived cyclic imines with acetylenedicarboxylates has been developed. The reaction works quite efficiently under very mild conditions to afford benzo[g][1,2,3]oxathiazocine-4,5-dicarboxylate 2,2-dioxide derivatives in high yields. Copyright
