3968-68-1Relevant academic research and scientific papers
Phosphonate-Directed Catalytic Asymmetric Hydroboration: Delivery of Boron to the More Substituted Carbon, Leading to Chiral Tertiary Benzylic Boronic Esters
Chakrabarty, Suman,Takacs, James M.
, p. 10530 - 10536 (2018/10/25)
Phosphonate-directed catalytic asymmetric hydroboration (CAHB) of β-aryl/heteroaryl methylidenes and trisubstituted alkenes by pinacolborane enables facile access to functionalized, chiral tertiary benzylic boronic esters. Hydroboration is catalyzed by a chiral rhodium catalyst prepared in situ from a Rh(I) precursor in combination with a simple TADDOL-derived chiral cyclic monophosphite in a 1:1 ratio. The regio- and stereochemistry arise from the combined effects of the relative disposition of the directing group to the alkene, the alkene substitution pattern, and the necessity of an aryl substituent attached to the alkene. A range of aryl and heteroaryl substituents can be accommodated, and for several chiral substrates, the reactions are efficiently catalyst-controlled, enabling the choice of diastereomeric products as desired. Stereospecific transformations of the chiral boronic ester afford chiral phosphonates bearing a quaternary carbon stereocenter. The synthetic utility of the products is further demonstrated by α-oxidation of the phosphonate, leading to hydroxy- and oxophosphonates; the latter readily undergo elimination/substitution reactions to unmask the phosphonate functionality with the formation of aldehydes, alcohols, esters, amides, acids, and ketones.
Lithium enolates in the enantioselective construction of tetrasubstituted carbon centers with chiral lithium amides as noncovalent stereodirecting auxiliaries
Yu, Kai,Lu, Ping,Jackson, Jeffrey J.,Nguyen, Thuy-Ai D.,Alvarado, Joseph,Stivala, Craig E.,Ma, Yun,Mack, Kyle A.,Hayton, Trevor W.,Collum, David B.,Zakarian, Armen
supporting information, p. 527 - 533 (2017/05/19)
Lithium enolates derived from carboxylic acids arc 0 0 OH ubiquitous intermediates in organic synthesis. Asymmetric transformations with these intermediates, a central goal of organic synthesis, are typically carried out with covalently attached chiral 0 auxiliaries. An alternative approach is to utilize chiral reagents that form discrete form discrete, well-defined aggregates with lithium enolates, H' 0 R3 0 providing a chiral environment conducive of asymmetric bond 98°6 ee formation. These reagents effectively act as noncovalent, or R' = OMe. Me good yields RI traceless, chiral auxiliaries. Lithium amides are an obvious choice Michael addition for such reagents as they are known to form mixed aggregates with lithium enolates. We demonstrate here that mixed aggregates can chiral directing reagent readily recovered in >95% yield effect highly enantioselective transformations of lithium enolates in several classes of reactions, most notably in transformations forming tetrasubstituted and quaternary carbon centers. Easy recovery of the chiral reagent by aqueous extraction is another practical advantage of this one-step protocol. Crystallographic, spectroscopic, and computational studies of the central reactive aggregate, which provide insight into the origins of selectivity, are also reported.
Modular, catalytic enantioselective construction of quaternary carbon stereocenters by sequential cross-coupling reactions
Potter, Bowman,Edelstein, Emma K.,Morken, James P.
, p. 3286 - 3289 (2016/07/13)
The catalytic Suzuki-Miyaura cross-coupling with chiral γ,γ-disubstituted allylboronates in the presence of RuPhos ligand occurs with high regioselectivity and enantiospecificity, furnishing nonracemic compounds with quaternary centers. Mechanistic experiments suggest that the reaction occurs by transmetalation with allyl migration, followed by rapid reductive elimination.
Entrapment of a chiral cobalt complex within silver: A novel heterogeneous catalyst for asymmetric carboxylation of benzyl bromides with CO2
Yang, Heng-Pan,Yue, Ying-Na,Sun, Qi-Long,Feng, Qiu,Wang, Huan,Lu, Jia-Xing
supporting information, p. 12216 - 12219 (2015/07/27)
A novel way to accommodate heterogeneous catalysis, CO2 fixation and asymmetric synthesis on one catalyst is reported. The [Co]@Ag composite was prepared for the first time and used for asymmetric carboxylation of benzyl bromides with CO2. All the procedures were performed under mild conditions. Moreover, the [Co]@Ag composite has terrific stability and reusability.
Catalytic asymmetric synthesis using feedstocks: An enantioselective route to 2-arylpropionic acids and 1-arylethyl amines via hydrovinylation of vinyl arenes
Smith, Craig R.,Babu, T.V. Rajan
experimental part, p. 3066 - 3072 (2009/08/08)
A three-step procedure for the synthesis of 2-arylpropionic acids (profens) from vinyl arenes in nearly enantiomerically pure form has been developed. Excellent yields (>97%), regioselectivities (>99%), and enantioselectivities (>97% ee) for the desired branched products were obtained in the asymmetric hydrovinylation reactions of vinyl arenes, and the products from these reactions were transformed into 2-arylpropionic acids via oxidative degradation. Subsequent Curtius or Schmidt rearrangements of these acids provided highly valued 1-arylethyl amines, including a prototypical primary amine with an α-chiral tertiary N-alkyl group, in very good yields.
Enantioselective synthesis of nitroalkanes bearing all-carbon quaternary stereogenic centers through Cu-catalyzed asymmetric conjugate additions
Wu, Jing,Mampreian, Dawn M.,Hoveyda, Amir H.
, p. 4584 - 4585 (2007/10/03)
The first examples of catalytic asymmetric conjugate addition (ACA) of alkylzinc reagents to trisubstituted nitroalkenes, leading to the formation of nitroalkanes bearing a quaternary carbon stereogenic center, are reported. Reactions are promoted in the
Synthesis and photochemistry of (2S,4R)- and (2R,4R)-1,2,3,4-tetrahydro-4-ethyl-1,1,4-trimethyl-3Z-ethylidene-2-naphthalenols
Miesen, F. W. A. M.,Dongen, J. L. J. van,Meijer, E. W.
, p. 307 - 317 (2007/10/02)
The synthesis and photochemistry of optically pure (2S,4R)- and (2R,4R)-1,2,3,4-tetrahydro-4-ethyl-1,1,4-trimethyl-3Z-ethyliden-2-naphthalenols 10a and 11a are described.Naphthalenols 10a and 11a were prepared in seven steps from 2-phenylbutanenitrile.Syn
