SN2 type hydrolysis of secondary alkyl halides and sulfonates in hydrothermal water

Yamasaki, Yuki,Hirayama, Takaharu,Oshima, Koichiro,Matsubara, Seijiro

, p. 864 – 865 (2004)

Optically active secondary alkyl halides and sulfonates were treated with alkaline hydrothermal water at 250°C in sealed vessel. The hydrolysis mostly proceeded with inversion of stereochemistry.

Activation of Epoxides by a Cooperative Iron-Thiolate Catalyst: Intermediacy of Ferrous Alkoxides in Catalytic Hydroboration

Song, Heng,Ye, Ke,Geng, Peiyu,Han, Xiao,Liao, Rongzhen,Tung, Chen-Ho,Wang, Wenguang

, p. 7709 – 7717 (2017)

This paper describes a cooperative iron-thiolate catalyst Cp?Fe(1,2-Ph2PC6H4S)(NCMe) (Cp?- = C5Me5-, [1(NCMe)]) for regioselective hydroboration of aryl epoxide by pinacolborane (HBpin). The critical catalytic step involves the direct addition of epoxide to the catalyst rather than activation of the B-H bond of HBpin. Through iron-thiolate cooperation, [1(NCMe)] opens the aryl epoxide rings affording ferrous-alkoxide compounds. Notably, the ferrous-alkoxide intermediate (4) was structurally characterized after its isolation from the reaction of [1(NCMe)] with trans-2,3-diphenyloxirane. The more Lewis acidic hydroboranes such as H3B·THF and 9-BBN (BBN = borabicyclononane) can also be captured by [1(NCMe)]. The resulting iron-borane adducts [1H(BH2)] and [1H(BBN)] feature an agnostic Fe···B-H interaction. DFT calculations indicate that the addition of HBpin across the iron-thiolate sites is endergonic by 12.9 kcal/mol, whereas it is exergonic by 20.2 kcal/mol with BH3 and 4.6 kcal/mol with 9-BBN. Combining the experimental data with theoretical studies, a mechanism of the substrate activation by [1(NCMe)], followed by HBpin addition, is proposed for the catalysis.

Selective Reductions. 32. Structural Effects on the reduction of Epoxides by Lithium Triethylborohydride. A Kinetic Study

Brown, Herbert C.,Narasimhan, S.,Somayaji, Vishwanatha

, p. 3091 – 3096 (1983)

An analytical procedure for the estimation of lithium triethylborohydride utilizing iodimetry has been developed.The rates of reduction of a number of epoxides are studied.The reaction exhibits second-order kinetics, first order with respect to each reactant.Methyl substitution decreases the reactivity of the epoxide by a factor of 8-10.In the case of aliphatic derivatives, the cis epoxide reacts 12 times faster than the trans.On the other hand, cis- and trans-β-methylstyrene oxides exhibit the opposite trend.A remarkable change in the regioselectivity of reduction of these two epoxides was observed.A possible explanation is presented.The kinetic isotope effect has been established both by rate studies and by determination, by mass spectrometry, of the deuterium incorporation in a competitive reaction between LiEt3BH, LiEt3BD, and the epoxide.A value of kH/kD ca. 1.4-1.5 is obtained by both methods.A mechanism is proposed to account for these results.

Chemo- and regioselective Meerwein-Ponndorf-Verley and Oppenauer reactions catalyzed by Al-free Zr-zeolite beta

Zhu, Yongzhong,Chuah, Gaikhuan,Jaenicke, Stephan

, p. 1 – 10 (2004)

Al-free Zr-beta zeolite with Si/Zr up to 75 was synthesized in a fluoride medium. The incorporation of zirconium into zeolite beta induced the formation of increased amounts of polymorph B. Lewis acid sites were predominant in the Al-free Zr-beta. Zr-zeolite beta was an excellent catalyst in the Meerwein-Ponndorf-Verley (MPV) reduction of several alkyl- and aryl-substituted cyclohexanones, with high selectivity to the corresponding alcohols. The catalyst was reusable and no leaching was detected under the reaction conditions. A prominent feature of the Zr-zeolite beta catalyst was its ability to maintain activity even in the presence of rather significant amounts of water, ≤ 9 wt%. The high catalytic ability of Zr-beta zeolites for the MPV reaction was attributed to the presence of Lewis acid sites with appropriate acid strength and to the ease of ligand exchangeability of Zr. Zr-zeolite beta had predominantly Lewis acidity with higher Lewis acid strength than that of Ti- and Sn-zeolite beta, which enabled Zr-zeolite beta to bind the carbonyl group effectively. Regeneration of the catalyst after poisoning by benzoic acid can be effected by thorough washing with 2-propanol. The sample showed good tolerance to the presence of water and pyridine.

Instantaneous SmI2-H2O-mediated reduction of dialkyl ketones induced by amines in THF

Dahlén, Anders,Hilmersson, G?ran

, p. 7197 – 7200 (2002)

Reduction of various ketones to their corresponding alcohols is shown to be instantaneous, i.e. completed in less than 10 s, by samarium diiodide (2.5 equiv.) in the presence of water (6.25 equiv.) and an amine (5 equiv.) in THF. The rates of reduction of ketones in this mixture exceed by far the rates determined by an amine or water alone. Rate enhancement is at least 100 000 compared to the reduction without a proton source, or at least 100 times faster than the rate of the widely used HMPA/alcohol accelerated reductions. This new method is therefore suggested to be an excellent replacement of the toxic HMPA/alcohol method.

Asymmetric Catalyses, XXXIX: Monohydrosilanes in the Enantioselective Catalytical Hydrosilylation of Prochiral Ketones

Brunner, Henri,Fisch,Heinrich

, p. 525 – 532 (1988)

The reactivity of several monohydrosilane/complex systems in the hydrosilylation of acetophenone and benzylmethylketone was investigated.The active systems were modified by addition of optically active ligands and used as enantioselective in-situ catalysts for the hydrosilylation of the above prochiral ketones which on hydrolysis gave α-phenylethanol and α-benzylethanol in up to 18percent ee. – Keywords: Monohydrosilanes; Enantioselective hydrosilylation; Prochiral ketones

Synthesis of (R)-selegiline via hydrolytic kinetic resolution

Kondekar, Nagendra B.,Kumar, Pradeep

, p. 1301 – 1308 (2011)

A short and enantioselective formal synthesis of (R)-selegiline has been achieved using Jacobsen’s hydrolytic kinetic resolution (HKR) of phenyl propylene oxide.

Synthesis of a novel magnetic nanocatalyst based on rhodium complex for transfer hydrogenation of ketone

Kooti,Nasiri

, (2019)

A magnetic heterogeneous nanocatalyst based on novel rhodium complex is designed.?The transfer hydrogenation of ketones with 2-propanol as hydrogen donor and the rhodium complex as nanocatalyst was achieved. High yields of ketones under mild conditions were obtained from easily available precursors.

Chemo-enzymatic synthesis of the active enantiomer of the anorressant 2- benzylmorpholine

D’Arrigo, Paola,Lattanzio, Maria,Fantoni, Giuseppe Pedrocchi,Servi, Stefano

, p. 4021 – 4026 (1998)

Baker’s yeast reduction of (Z)-α-bromocinnamaldehyde 1 in the presence of absorbing resins allows the easy preparation of the corresponding saturated bromo-alcohol 2 in high yields and enantiomeric excess. The absolute configuration is assigned through conversion into the (R)-phenyl oxirane 3 and 1-phenyl-2-propanol 4 of (S) absolute configuration. The (R)- epoxide is transformed into 6, the pharmacologically active enantiomer of the appetite suppressant 2-benzylmorpholine, to which the (R) configuration is assigned.

Regiodivergent Reductive Opening of Epoxides by Catalytic Hydrogenation Promoted by a (Cyclopentadienone)iron Complex

De Vries, Johannes G.,Gandini, Tommaso,Gennari, Cesare,Jiao, Haijun,Pignataro, Luca,Stadler,

The reductive opening of epoxides represents an attractive method for the synthesis of alcohols, but its potential application is limited by the use of stoichiometric amounts of metal hydride reducing agents (e.g., LiAlH4). For this reason, the corresponding homogeneous catalytic version with H2 is receiving increasing attention. However, investigation of this alternative has just begun, and several issues are still present, such as the use of noble metals/expensive ligands, high catalytic loading, and poor regioselectivity. Herein, we describe the use of a cheap and easy-To-handle (cyclopentadienone)iron complex (1a), previously developed by some of us, as a precatalyst for the reductive opening of epoxides with H2. While aryl epoxides smoothly reacted to afford linear alcohols, aliphatic epoxides turned out to be particularly challenging, requiring the presence of a Lewis acid cocatalyst. Remarkably, we found that it is possible to steer the regioselectivity with a careful choice of Lewis acid. A series of deuterium labeling and computational studies were run to investigate the reaction mechanism, which seems to involve more than a single pathway.