72203-35-1Relevant articles and documents
Planar chiral PHANOLs as double hydrogen bonding donor organocatalysts: Synthesis and catalysis
Braddock, D. Christopher,MacGilp, Iain D.,Perry, Benjamin G.
, p. 1117 - 1130 (2004)
4,12-Dihydroxy[2.2]paracyclophanediol (PHANOL; 1), and its para-substituted derivatives 2, 5 and 7, were found to catalyse Diels-Alder cyclo-additions of α,β-unsaturated aldehydes or ketones with dienes and/or epoxide ring opening reactions with amines. The mode of catalysis by the PHANOLs is via double hydrogen bonding to the two sp2 lone pairs of a carbonyl group or the two lone pairs of the epoxide. The order of activity of the PHANOLs for catalysis of the Diels-Alder reaction essentially correlates with the expected hydrogen-bond donor strength based on the degree of electron-withdrawing capability of the group(s) in the para position. In contrast, ortho-substituted PHANOLs 10, 11 and 14 were not active as catalysts due to steric interference with the double hydrogen bonding mode. 1H NMR and IR spectral data for the various PHANOLs are discussed in support of the proposed double hydrogen bond mode.
Bis-selenonium Cations as Bidentate Chalcogen Bond Donors in Catalysis
He, Xinxin,Wang, Xinyan,Tse, Ying-Lung Steve,Ke, Zhihai,Yeung, Ying-Yeung
, p. 12632 - 12642 (2021/10/21)
Lewis acids are frequently employed in catalysis but they often suffer from high moisture sensitivity. In many reactions, catalysts are deactivated because of the problem that strong Lewis acids also bond to the products. In this research, hydrolytically stable bidentate Lewis acid catalysts derived from selenonium dicationic centers have been developed. The bis-selenonium catalysts are employed in the activation of imine and carbonyl groups in various transformations with good yields and selectivity. Lewis acidity of the bis-selenonium salts was found to be stronger than that of the monoselenonium systems, attributed to the synergistic effect of the two cationic selenonium centers. In addition, the bis-selenonium catalysts are not inhibited by strong bases or moisture.
Ruthenium Lewis Acid-Catalyzed Asymmetric Diels–Alder Reactions: Reverse-Face Selectivity for α,β-Unsaturated Aldehydes and Ketones
Thamapipol, Sirinporn,Ludwig, Bettina,Besnard, Céline,Saudan, Christophe,Kündig, E. Peter
, p. 774 - 789 (2016/10/17)
Acrolein, methacrolein, methyl vinyl ketone, ethyl vinyl ketone, 3-methyl-3-en-2-one, and divinyl ketone were coordinated to a cationic cyclopentadienyl ruthenium(II) Lewis acid incorporating the electron-poor bidentate BIPHOP–F ligand. Analysis by NOESY and ROESY NMR techniques allowed the determination of conformations of enals and enones present in solution in CD2Cl2. The results were compared to solid-state structures and to the facial selectivities of catalytic asymmetric Diels–Alder reactions with cyclopentadiene. X-Ray structures of four Ru-enal and Ru-enone complexes show the α,β-unsaturated C=O compounds to adopt an anti-s-trans conformation. In solution, enals assume both anti-s-trans and anti-s-cis conformations. An additional conformation, syn-s-trans, is present in enone complexes. Enantioface selectivity in the cycloaddition reactions differs for enals and enones. Reaction products indicate enals to react exclusively in the anti-s-trans conformation, whereas with enones, the major product results from the syn-s-trans conformation. The alkene in s-cis conformations, while present in solution, is shielded and cannot undergo cycloaddition. A syn-s-trans conformation is found in the solid state of the bulky 6,6-dimethyl cyclohexanone-Ru(II) complex. The X-ray structure of divinyl ketone is unique in that the Ru(II) center binds the enone via a η2bond to one of the alkene moieties. In solution, coordination to Ru–C=O oxygen is adopted. A comparison of facial preference is also made to the corresponding indenyl Lewis acids.
