21592-97-2Relevant academic research and scientific papers
Bismuth-substituted "sandwich" type polyoxometalate catalyst for activation of peroxide: Umpolung of the peroxo intermediate and change of chemoselectivity
Amanchi, Srinivasa Rao,Khenkin, Alexander M.,Diskin-Posner, Yael,Neumann, Ronny
, p. 3336 - 3341 (2015/06/16)
The epoxidation of alkenes with peroxides by WVI, MoVI, VV, and TiIV compounds is well established, and it is well accepted that the active intermediate peroxo species are electrophilic toward nucleophilic substrates. Polyoxotungstates, for example, those of the "sandwich" structure, [WZn(TM-L)2(ZnW9O34)2]q- in which TM = transition metal and L = H2O, have in the past been found to be excellent epoxidation catalysts. It has now been found that substituting the Lewis basic BiIII into the terminal position of the "sandwich" polyoxometalate structure to yield [Zn2BiIII2(ZnW9O34)2]14- leads to an apparent umpolung of the peroxo species and formation of a nucleophilic peroxo intermediate. There are two lines of evidence that support the formation of a reactive nucleophilic peroxo intermediate: (1) More electrophilic sulfoxides are more reactive than more nucleophilic sulfides, and (2) nonfunctionalized aliphatic alkenes and dienes showed ene type reactivity rather than epoxidation pointing toward "dark" formation of singlet oxygen from the nucleophilic intermediate peroxo species. Allylic alcohols reacted much faster than alkenes but showed chemoselectivity toward C-H bond activation of the alcohol and formation of aldehydes or ketones rather than epoxidation. This explained via alkoxide formation at the BiIII center followed by oxidative β-elimination.
Studies on difficult intramolecular hydroaminations in the context of four syntheses of alkaloid natural products
Dion, Isabelle,Vincent-Rocan, Jean-Francois,Zhang, Lei,Cebrowski, Pamela H.,Lebrun, Marie-Eve,Pfeiffer, Jennifer Y.,Bedard, Anne-Catherine,Beauchemin, Andre M.
, p. 12735 - 12749 (2014/01/17)
Examples of intramolecular alkene hydroaminations forming six-membered ring systems are rare, especially for systems in which the double bond is disubstituted. Such cyclizations have important synthetic relevance. Herein we report a systematic study of these cyclizations using recently developed Cope-type hydroamination methodologies. Difficult intramolecular alkene hydroaminations were used as key steps in syntheses of 2-epi-pumiliotoxin C, coniine, N-norreticuline and desbromoarborescidine A. This effort required the development of optimized hydroamination conditions to improve the efficiency of the cyclizations. Collectively, our results show that Cope-type cyclizations can be achieved on a variety of challenging substrates and proceed under similar conditions for both N-H and N-substituted hydroxylamines.
Regioselective SN2 opening of vinylic epoxides with trialkylzincates and trialkylaluminates
Equey, Olivier,Vrancken, Emmanuel,Alexakis, Alexandre
, p. 2151 - 2159 (2007/10/03)
The use of trialkylorganozincates and tetraalkylaluminates allows regioselective SN2 nucleophilic opening of vinylic epoxides. The reaction occurs with an anti-substitution pattern and can be applied to a wide range of substrates. We also show that the solvent and the structure of the epoxide have an influence on the substitution products' ratio. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
Enantioselective opening of cyclic vinyl epoxides with organoaluminium reagents catalysed by copper salts
Equey, Olivier,Alexakis, Alexandre
, p. 1531 - 1536 (2007/10/03)
Herein we report conditions for the enantioselective conjugate addition of trialkylaluminium reagents to cyclic vinyl epoxides catalysed by copper salts and chiral phosphorus-based ligands. The reaction must be carried out in THF, otherwise we observed only oligomeric products. The best ees have been obtained with CuTC as the copper salt and a 2,2′-binaphthyl-based phosphorus ligand. Both opening products (SN2 and SN2 ′ pathways) were obtained with good enantioselectivity and moderate to good regioselectivity.
Regioselectivity in the palladium-catalyzed addition of carbon nucleophiles to carbocyclic derivatives
Hoke, Molly E.,Brescia, Marc-Raleigh,Bogaczyk, Suzanne,DeShong, Philip,King, Bryan W.,Crimmins, Michael T.
, p. 327 - 335 (2007/10/03)
The regioselectivity of Pd-catalyzed malonate additions and arylations to cycloalkenyl esters can be predicted by completing a stereochemical analysis of the Pd-π-allyl complex. The Pd-catalyzed malonate additions which have the greatest degree of regioselectivity are in which substituents have a steric influence in blocking the incoming nucleophile. Cyclopentenyl substrates displayed lower regioselectivity than the cyclohexyl counterparts presumably due to increased planarity of the system. Arylations using tin and hypervalent silicon reagents were compared.
A multigram, catalytic and enantioselective synthesis of optically active 4-methyl-2-cyclohexen-1-one: A useful chiral building block
Bertozzi,Crotti,Feringa,Macchia,Pineschi
, p. 483 - 486 (2007/10/03)
The first catalytic asymmetric synthesis of both (R)-(+)- and (S)-(-)-4-methyl-2-cyclohexen-1-one and a new and improved synthesis of both enantiomers of (1S,4S)-(-) and (1R,4R)-(+)-4-methyl-2-cyclohexen-1-o1 was developed on a multigram scale. The key step of this approach is the asymmetric catalyzed addition of Me2Zn (SN2′-pathway) to racemic 1,3-cyclohexadiene monoepoxide. This step has been optimized as for as enantio- and regioselectivities, and work-up procedures. The striking ligand accelerated catalysis exhibited by the chiral copper complex of the 2,2′-binaphthyl-based phosphoramidite, herein reported, permitted a very low catalyst loading (0.6 mol%).
A Facile and Selective 1,2-Reduction of Conjugated Ketones with NaBH4 in the Presence of CaCl2
Fujii, Hideaki,Oshima, Koichiro,Utimoto, Kiitiro
, p. 1847 - 1848 (2007/10/02)
CaCl2 is an efficient catalyst for the regioselective 1,2-reduction of α-enones with NaBH4 in methanol solution.
Oxidation by Cobalt(III) Acetate. Part 7. Regioselective Synthesis of Substituted Cyclohexenyl Acetates
Hirano, Masao,Morimoto, Takashi
, p. 1105 - 1108 (2007/10/02)
The oxidation of alkylcyclohexenes with cobalt(III) acetate has been studied in acetic acid under nitrogen. 1-Alkylcyclohexenes gave exclusively the corresponding 3-acetoxy-1-alkylcyclohexenes in good yields.Similarly, 3- and 4-methylcyclohexene afforded 3-acetoxy-6- and -5-methylcyclohexene, respectively, in suprising high selectivities.In all cases, the position α to the alkyl group was completely or largely insensitive to CoIII.The results can be explained in terms of steric hindrance of the alkyl group which limits the attack of CoIII at a hindered site.
