84276-14-2Relevant academic research and scientific papers
Mechanistic Insights into Enantioselective C-H Photooxygenation of Aldehydes via Enamine Catalysis
Walaszek, Dominika J.,Rybicka-Jasińska, Katarzyna,Smoleń, Sabina,Karczewski, Maksymilian,Gryko, Dorota
supporting information, p. 2061 - 2070 (2015/06/23)
Organocatalytic photooxygenation of aldehydes at the α-position proceeds via enamine catalysis, though enamines should be easily oxidized by singlet oxygen respectively to amides and carbonyl compounds. Moreover, the formation of a zwitterionic enamine peroxide intermediate was postulated based on experimental and theoretical data. The reaction affords desired diols (after in situ reduction) in a decent yield and (S)- or (R)-enantioselectivity depending on a catalyst used. The (S)-enantiomer predominated in imidazolidinone-catalyzed reactions, while prolineamides assured the formation of the (R)-stereoisomer. DFT calculation suggests that the enamine-oxygen complex with the lowest energy has the E,s-cis conformation for the prolineamide derivative and E,s-trans for the imidazolidinone catalyst, explaining the opposite stereoselectivity in the photooxygenation reaction.
A recyclable dendritic osmium catalyst for homogeneous dihydroxylation of olefins
Fujita, Ken-Ichi,Yamazaki, Manabu,Ainoya, Taku,Tsuchimoto, Teruhisa,Yasuda, Hiroyuki
experimental part, p. 8536 - 8543 (2010/11/18)
A series of osmate (OsO42-) core dendrimers was prepared by an ion-exchange technique through the mixing of K 2OsO4 and a bis(quaternary ammonium bromide) core dendrimer, which consisted of poly(benzyl ether) dendron. By employing an osmate core dendrimer as a homogeneous catalyst, dihydroxylation reactions of olefins proceeded rapidly, and the dendritic osmium catalyst was recovered by reprecipitation and then reused. Furthermore, a dendritic effect on the recyclability of a catalyst was observed. In the case of asymmetric dihydroxylation reactions, the corresponding diol was obtained in a high chemical yield with a fair enantiomeric excess (ee). In this case, not only the dendritic osmium catalyst but also the chiral ligand could be recovered by reprecipitation and reused efficiently up to five times.
Methanesulfonamide: A cosolvent and a general acid catalyst in sharpless asymmetric dihydroxylations
Junttila, Mikko H.,Hormi, Osmo O.E.
experimental part, p. 3038 - 3047 (2009/08/08)
To obtain information about the effect that methanesulfonamide has in the hydrolysis step in Sharpless asymmetric dihydroxylation, a series of aliphatic and conjugated aromatic olefins were dihydroxylated with and without methanesulfonamide. The hypothesis in this study was that methanesulfonamide is a cosolvent that aids in the transfer of the hydroxide ions from the water phase to the organic phase. A plot of t90% versus the computational partition coefficient clog P of the intermediate osmate ester of nonterminal aliphatic olefins revealed that the polarity of the intermediate osmate ester has a significant effect on the reaction time and methanesulfonamide effect. The more polar the intermediate osmate ester, the faster is the reaction without methanesulfonamide and the smaller the accelerating methanesulfonamide effect. Methanesulfonamide had no accelerating effect in the asymmetric dihydroxylation of short chain terminal aliphatic olefins as a result of easier accessibility of terminal osmate ester groups to the water phase. A cosolvent hypothesis was found not to be valid in asymmetric dihydroxylations of conjugated aromatic olefins. In the reaction conditions used in Sharpless asymmetric dihydroxylation, weakly acidic methanesulfonamide was found to be a general acid catalyst that protonates the intermediate osmate esters of conjugated aromatic olefins in the hydrolysis step.
Formal alkyne aza-prins cyclization: Gold(I)-catalyzed cycloisomerization of mixed N,O-acetals generated from homopropargylic amines to highly substituted piperidines
Cheoljae, Kim,Hyo, Jin Bae,Ji, Hyung Lee,Wook, Jeong,Haejin, Kim,Sampath, Vasu,Young, Ho Rhee
supporting information; experimental part, p. 14660 - 14661 (2010/02/28)
(Chemical Equation Presented). A new gold(I)-catalyzed cycloisomerization to access highly substituted piperidines has been developed. By combining a conceptually new way of generating iminium ions using cationic gold(I) complexes and an efficient cyclization reaction that can minimize a potentially competing aza-Cope rearrangement, the proposed reaction successfully circumvents a long-standing problem in the classical aza-Prins reaction. Synthetic utility of the catalytic reaction was demonstrated by a synthesis of optically active 2-alkyl-piperidin-4-one.
Rh-catalyzed enantioselective diboration of simple alkenes: Reaction development and substrate scope
Trudeau, Stephane,Morgan, Jeremy B.,Shrestha, Mohanish,Morken, James P.
, p. 9538 - 9544 (2007/10/03)
The rhodium-catalyzed reaction between bis(catecholato)diboron and simple alkenes results in the syn addition of the diboron across the alkene. The resulting 1,2-bis(boronate) is subsequently oxidized to provide the 1,2-diol. In the presence of enantiomerically enriched Quinap ligand, high enantioselection in the diboration can be achieved. The reaction is highly selective for trans- and trisubstituted alkenes and can be selective for some monosubstituted alkenes as well. The development of this reaction is described as is the substrate scope and experiments that are informative about the reaction mechanism and competing pathways.
An electrophilic cleavage procedure for the asymmetric dihydroxylation: Direct enantioselective synthesis of cyclic boronic esters from olefins
Hoevelmann, Claas H.,Muniz, Kilian
, p. 3951 - 3958 (2007/10/03)
A variation within the osmium-catalysed asymmetric dihydroxylation (AD) of olefins is described that yields cyclic boronic esters from olefins in a straight-forward manner. This process represents the first real product alteration in asymmetric dihydroxylation, since all previous protocols lead to free diols exclusively. A protocol based on the Sharpless AD conditions (for enantioselective oxidation of prochiral olefins) was developed that gives cyclic boronic esters with excellent enantiomeric excesses (ee's). Some of the ee's are higher than those reported for conventional AD. The unprecedented role of phenyl boronic acid on the course of the AD reaction was investigated in detail. PhB(OH)2 does not interfere with the chiral ligand. leaving the enantioselective step of olefin oxidation intact. The main role of the boronic acids - apart from protecting the diol products against potential overoxidation-relies on removing the diol entity in an electrophilic cleavage, which is in contrast to the conventional hydrolylic cleavage of the AD protocols. Thus, a mechanistically new cleavage for enantioselective dihydroxylation reactions is introduced within the present work.
Catalytic Asymmetric Carbohydroxylation of Alkenes by a Tandem Diboration/Suzuki Cross-Coupling/Oxidation Reaction
Miller, Steven P.,Morgan, Jeremy B.,Nepveux V, Felix J.,Morken, James P.
, p. 131 - 133 (2007/10/03)
(Equation presented) Chiral nonsymmetric 1,2-diboron adducts are generated by catalytic enantioselective diboration. Oxidation of these adducts provides 1,2-diols in good yield. Alternatively, 1,2-diboron compounds may be reacted, in situ, with aryl halides wherein the less hindered C-B bond participates in cross-coupling. The remaining C-B bond is then oxidized in the reaction workup thereby allowing for net asymmetric carbohydroxylation of alkenes in a tandem one-pot diboration/Suzuki coupling/oxidation sequence.
Catalytic Asymmetric Dihydroxylation of Aliphatic Olefins with Reusable Resin-Osmium Tetroxide
Choudary, Boyapati M.,Jyothi, Karangula,Madhi, Sateesh,Kantam, M. Lakshmi
, p. 1190 - 1192 (2007/10/03)
Asymmetric dihydroxylation of aliphatic olefins to chiral diols with good yields and ees by a heterogeneous Resin-OsO4 catalyst using ferricyanide as cooxidant is disclosed for the first time. The catalyst was recovered quantitatively by simple filtration and reused for several times without significant loss of activity.
Catalytic asymmetric dihydroxylation of C,C double bonds with osmium tetroxide using selenoxides as co-oxidants
Krief,Castillo-Colaux
, p. 501 - 504 (2007/10/03)
Asymmetric dihydroxylation of olefins has been achieved in good yields and ee's using potassium osmate dihydrate (K2OsO2(OH)4, the pre-oxidant), (DHQD)2PHAL (the chiral ligand), potassium carbonate (the base) and selenoxides (the co-oxidants). Both the yield and the ee proved to be pH dependent, the highest yield and ee being found at almost the same pH values. The rate of the reaction was found to be highly dependent upon the structure of the selenoxide used. Some representative examples involving aminoxides are presented for comparison.
New polymer supported cinchona alkaloids for heterogeneous catalytic asymmetric dihydroxylation of olefins
Nandanan,Sudalai,Ravindranathan
, p. 2577 - 2580 (2007/10/03)
Two new polymeric cinchona alkaloid derived ligands were synthesized and utilized in the asymmetric dihydroxylation of olefins, exhibiting high enantioselectivities in the case of aliphatic terminal olefins under heterogeneous phase.
