Directed reduction of .beta.-hydroxy ketones employing tetramethylammonium triacetoxyborohydride
作者:D. A. Evans、K. T. Chapman、E. M. Carreira
DOI:10.1021/ja00219a035
日期:1988.5
The mild reducing agent tetramethylammonium triacetoxyborohydride reduces acyclic P-hydroxy ketones to their corresponding anti diols with high diastereoselectivity. a-Alkyl substitution does not significantly affect the stereoselectivity of these reductions. In all cases examined, good to excellent yields of diastereomerically homogeneous diols were obtained. The mechanism of these reductions involves
温和的还原剂四甲基铵三乙酰氧基硼氢化物以高非对映选择性将无环 P-羟基酮还原为其相应的反二醇。α-烷基取代不会显着影响这些还原的立体选择性。在所有检查的情况下,都获得了良好到极好的非对映异构体均质二醇的产率。这些还原的机制涉及三乙酰氧基硼氢化物阴离子将乙酸盐与底物醇进行酸促进的配体交换。所得氢化物中间体,大概是烷氧基二乙酰氧基硼氢化物,还原近端 OH 0 OH OH 0 Me,NHB(OAc), Mew Me&OR - OR Me he
Highly efficient enantio-differentiating hydrogenation over an ultrasonicated raney nickel catalyst modified with tartaric acid
A tartaric acid–NaBr-modified Raney nickel catalyst prepared from ultrasonicated Raney nickel showed excellent enantio-differentiating and hydrogenating activity in the hydrogenation of a series of 3-oxoalkanoate and 1,3-diketones.
The ultrasonic irradiation of Raneynickelcatalyst in water followed by the removal of the resulting turbid supernatant gave an excellent nickelcatalyst (RNi-U) which generated an asymmetrically-modified nickelcatalyst. An EPMA (SEM-EDX) study indicated that RNi-U consisted of a fairly pure nickelsurface of homogeneous size. Tartaric acid–NaBr-modified RNi-U (TA–NaBr–MRNi-U) showed a high enantio-differentiating
Asymmetric Desymmetrization Based on an Intramolecular Haloetherification: A Highly Effective and Recyclable Chiral Nonracemic Auxiliary, 2-exo-Methyl-3-endo-phenyl-5-norbornene-2-carboxaldehyde, formeso-1,3- andmeso-1,4-Diols
作者:Hiromichi Fujioka、Tetsuya Fujita、Naoyuki Kotoku、Yusuke Ohba、Yasushi Nagatomi、Atsushi Hiramatsu、Yasuyuki Kita
DOI:10.1002/chem.200400444
日期:2004.11.5
A new chiralauxiliary, a 3-endo-phenyl norbornene aldehyde derivative, which is a crystalline, very stable, and easily handled, was developed for the desymmetrization of meso-1,3- and meso-1,4-diols. The key step of the method, an intramolecular bromoetherification, proceeded in a highly diastereoselective manner. A four-step sequence, 1) acetalization, 2) intramolecular bromoetherification followed
The application of difunctional organosilicon compounds to organic synthesis; 1,3-asymmetric induction in the reduction of β-hydroxy-ketones
作者:Saeed Anwar、Anthony P. Davis
DOI:10.1039/c39860000831
日期:——
A number of β-hydroxy-ketones were reduced to anti-1,3-diols with diastereoisomeric excesses exceeding 95%, by a method involving presumed intramolecular transfer of hydrogen from a silicon atom to the carbonyl carbon.