937-05-3Relevant articles and documents
Joris et al.
, p. 4759 (1968)
Reaction of Trialkylboranes with Sodium Diethyldihydroaluminate in the Presence of 1,4-Diazabicyclooctane. A Convenient, General Method for Preparation of Sodium Trialkylborohydrides
Hubbard, John L.,Fuller, Joseph C.,Jackson, Thomas C.,Singaram, Bakthan
, p. 8311 - 8316 (1993)
Trialkylboranes in tetrahydrofuran (THF) or diethyl ether (EE) solutions, including those with exceptionally large steric requirements, react readily with toluene solutions of sodium diethyldihydroaluminate in the presence of 1,4-diazabicyclooctane (DABCO) to yield the corresponding sodium trialkylborohydrides and diethylaluminum hydride.The diethylaluminum hydride precipitates from solution as its DABCO adduct, with the use of EE as solvent facilitating the separation.This reaction constitutes a convenient, general method for preparing sodium trialkylborohydrides.
Diastereoselectivity in gas-phase hydride reduction reactions of ketones
Artau, Alexander,Ho, Yeunghaw,Kenttaemaa, Hilkka,Squires, Robert R.
, p. 7130 - 7137 (1999)
The intrinsic diastereoselectivity of the reduction of a series of cyclic ketones by pentacoordinate silicon hydride ions was investigated in the gas phase with the use of the flowing afterglow-triple quadrupole technique. The percent axial reduction of 4-tert-butylcyclohexanone (1), 2-methylcyclohexanone (2), 3,3,5-trimethylcyclohexanone (3), norcamphor (4), 2-tert-butyl-1,3-dioxan-5-one (5), and 2-tert-butyl-1,3-dithian-5-one (6) was determined by collision-induced dissociation experiments. The results show that axial (exo) reduction dominates for 1, 2, and 4, whereas equatorial reduction is dominant for 3, 5, and 6. The trend observed for the reduction diastereoselectivity of compounds 1-4 and 6 matches their condensed-phase behavior; i.e., the percent axial reduction is reduced when steric hindrance of the ketones is increased (1, 99 ± 3%; 2, 68 ± 5; 3, 9 ± 3%). The remarkable consistency of the results obtained in the gas phase and in solution suggests that environmental effects are either unimportant or cancel out and that the reduction diastereoselectivity is a property that can be attributed to the intrinsic nature of the isolated reactants. Qualitatively, the predictions made by Houk et al. regarding the diastereoselectivity of the reduction of 5 and 6 in the gas phase were confirmed, i.e., a preferred equatorial approach of the hydride reducing agent. The preference of compound 5 to undergo equatorial reduction in the gas phase (33 ± 4% axial reduction) contrasts with the almost exclusive. axial reduction reported in solution (93%). This deviation is likely caused by the strong electrostatic repulsion between the nucleophilic hydride reagent and the ring heteroatoms in 5. Compound 6 exhibits an even stronger preference for equatorial reduction (16 ± 4% axial reduction), in agreement with experimental results obtained by others in the condensed phase. Earlier calculations predict an even stronger preference for equatorial reduction. These results are readily rationalized in terms of competition among steric, torsional, and electrostatic effects.
Trans-Selective and Switchable Arene Hydrogenation of Phenol Derivatives
Bergander, Klaus,Glorius, Frank,Heusler, Arne,Wollenburg, Marco
, p. 11365 - 11370 (2020/11/24)
A trans-selective arene hydrogenation of abundant phenol derivatives catalyzed by a commercially available heterogeneous palladium catalyst is reported. The described method tolerates a variety of functional groups and provides access to a broad scope of trans-configurated cyclohexanols as potential building blocks for life sciences and beyond in a one-step procedure. The transformation is strategically important because arene hydrogenation preferentially delivers the opposite cis-isomers. The diastereoselectivity of the phenol hydrogenation can be switched to the cis-isomers by employing rhodium-based catalysts. Moreover, a protocol for the chemoselective hydrogenation of phenols to cyclohexanones was developed.
Introduction of Cyclopropyl and Cyclobutyl Ring on Alkyl Iodides through Cobalt-Catalyzed Cross-Coupling
Andersen, Claire,Ferey, Vincent,Daumas, Marc,Bernardelli, Patrick,Guérinot, Amandine,Cossy, Janine
supporting information, p. 2285 - 2289 (2019/03/29)
A cobalt-catalyzed cross-coupling between alkyl iodides and cyclopropyl, cyclobutyl, and alkenyl Grignard reagents is disclosed. The reaction allows the introduction of strained rings on a large panel of primary and secondary alkyl iodides. The catalytic system is simple and nonexpensive, and the reaction is general, chemoselective, and diastereoconvergent. The alkene resulting from the cross-coupling can be transformed to substituted cyclopropanes using a Simmons-Smith reaction. The formation of radical intermediates during the coupling is hypothesized.
A Practical and Stereoselective In Situ NHC-Cobalt Catalytic System for Hydrogenation of Ketones and Aldehydes
Zhong, Rui,Wei, Zeyuan,Zhang, Wei,Liu, Shun,Liu, Qiang
supporting information, p. 1552 - 1566 (2019/06/14)
Homogeneous catalytic hydrogenation of carbonyl groups is a synthetically useful and widely applied organic transformation. Sustainable chemistry goals require replacing conventional noble transition metal catalysts for hydrogenation by earth-abundant base metals. Herein, we report how a practical in situ catalytic system generated by easily available pincer NHC precursors, CoCl2, and a base enabled efficient and high-yielding hydrogenation of a broad range of ketones and aldehydes (over 50 examples and a maximum turnover number [TON] of 2,610). This is the first example of NHC-Co-catalyzed hydrogenation of C=O bonds using flexible pincer NHC ligands consisting of a N-H substructure. Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized by fine-tuning of the steric bulk of pincer NHC ligands. Additionally, a bis(NHCs)-Co complex was successfully isolated and fully characterized, and it exhibits excellent catalytic activity that equals that of the in-situ-formed catalytic system. Catalytic hydrogenation is a powerful tool for the reduction of organic compounds in both fine and bulk chemical industries. To improve sustainability, more ecofriendly, inexpensive, and earth-abundant base metals should be employed to replace the precious metals that currently dominate the development of hydrogenation catalysts. However, the majority of the base-metal catalysts that have been reported involve expensive, complex, and often air- and moisture-sensitive phosphine ligands, impeding their widespread application. From a mixture of the stable CoCl2, imidazole salts, and a base, our newly developed catalytic system that formed easily in situ enables efficient and stereoselective hydrogenation of C=O bonds. We anticipate that this easily accessible catalytic system will create opportunities for the design of practical base-metal hydrogenation catalysts. A practical in situ catalytic system generated by a mixture of easily available pincer NHC precursors, CoCl2, and a base enabled highly efficient hydrogenation of a broad range of ketones and aldehydes (over 50 examples and up to a turnover number [TON] of 2,610). Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized in high selectivities. Moreover, the preparation of a well-defined bis(NHCs)-Co complex via this pincer NHC ligand consisting of a N-H substructure was successful, and it exhibits equally excellent catalytic activity for the hydrogenation of C=O bonds.
