72345-23-4Relevant articles and documents
Isolation of Racemic 2,4-Pentanediol and 2,5-Hexanediol from Commercial Mixtures of Racemic and Meso Isomers by way of Cyclic Sulfites
Caron, Gaetan,Kazlauskas, Romas J.
, p. 657 - 664 (1994)
Enantiomerically pure diols with C2 symmetry such as 2,3-butanediol, 1, 2,4-pentanediol, 2, and 2,5-hexanediol, 3, are useful chiral auxiliaries, but they are expensive because chemists lack good synthetic routes that eliminate both the meso isomer and one enantiomer.Enzymic resolutions efficiently separate the enantiomer, but do not remove the meso isomer.To simplify enzymic resolutions of 2 and 3, we developed simple methods to isolate the racemic isomer from commercial mixtures of racemic and meso isomers 1 or 2, the meso isomer selectivity reacted with SOCl2 to give a cyclic sulfite that was removed by column chromatography to leave (+/-)-2, 92percent de, 1.4 g, 55percent yield.For 3, both meso and racemic isomers reacted with SOCl2 to give cyclic sulfites, but the sulfite derived from the meso isomer rearranged to trans-2,5-dimethyltetrahydrofuran under acidic conditions.Hydrolysis of the remaining sulfite gave (+/-)-3, 84percent de, 1.1 g, 37percent yield.Resolution of (+/-)-2 and (+/-)-3 using lipase from Pseudomonas cepacia yielded (2R,4R)-2-diacetate, 78 percent ee, >97percent de, 40percent of theory and (2R,5R)-3-diacetate, 94percent ee, >97percent de, 47percent of theory.Previously reported acetylations of 2 and 3 by lipase from Candida antarctica (CAL) or by lipase from Pseudomonas sp. (Amonolipase AK) are more enantioselective and thus, the best route to enantiomerically and diastereomerically pure 2 and 3 is removal of the meso isomer by way of cyclic sulfites followed by resolution with CAL or Amano lipase AK.
Vinylidene Homologation of Boronic Esters and its Application to the Synthesis of the Proposed Structure of Machillene
Fordham, James M.,Grayson, Matthew N.,Aggarwal, Varinder K.
supporting information, p. 15268 - 15272 (2019/10/21)
Alkenyl boronic esters are important reagents in organic synthesis. Herein, we report that these valuable products can be accessed by the homologation of boronic esters with lithiated epoxysilanes. Aliphatic and electron-rich aromatic boronic esters provided vinylidene boronic esters in moderate to high yields, while electron-deficient aromatic and vinyl boronic esters were found to give the corresponding vinyl silane products. Through DFT calculations, this divergence in mechanistic pathway has been rationalized by considering the stabilization of negative charge in the C?Si and C?B bond breaking transition states. This vinylidene homologation was used in a short six-step stereoselective synthesis of the proposed structure of machillene, however, synthetic and reported data were found to be inconsistent.
WATER-INSOLUBLE RUTHENIUM CATALYST COMPOSITION FOR USE IN AQUEOUS HYDROGENATION REACTIONS
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, (2016/02/26)
The invention relates to a method for converting a precatalyst complex to an active catalyst complex, wherein the precatalyst complex and the active catalyst complex comprise a ruthenium atom and an optically active ligand that is insoluble in water, and the active catalyst complex furthermore comprises a monohydride and a water molecule. The method comprises the steps of providing water as an activation solvent system with a pH value equal or below 2, and solving said precatalyst complex, an acid, and hydrogen therein. The invention further relates to a method for manufacturing a catalyst composition, a method for hydrogenating a substrate molecule and a reaction mixture.
