Transfer Hydrogenation of Ethyl Levulinate to γ‐Valerolactone Catalyzed by Iron Complexes

Conversion of biomass‐derived ethyl levulinate to γ‐valerolactone is realized by using homogeneous iron‐catalyzed transfer hydrogenation (CTH). By utilizing Casey's catalyst and cheap isopropanol as hydrogen source, γ‐valerolactone can be generated in 95% yield. Addition of catalytic amount of base is important to achieve good yield.     

A Novel Organocatalytic Asymmetric Transfer Hydrogenation of α,β‐Unsaturated Aldehydes

α,β‐Unsaturated aldehydes reacted with diimide (diazene) in the presence of optically active ammonium salt 1 as a catalyst to give the corresponding saturated aldehydes in excellent yields and up to 98 : 2 er. Attractive features of the asymmetric transfer hydrogenation are its high yields, and chemo‐, and enantioselectivities.     

Highly Enantioselective Iridium‐Catalyzed Hydrogenation of α,β‐Unsaturated Esters

α,β‐Unsaturated esters have been employed as substrates in iridium‐catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic‐ and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals.     

Effects of Solid Acid Supports on the Bifunctional Catalysis of Levulinic Acid to γ‐Valerolactone: Catalytic Activity and Stability

Heterogeneous transformation of levulinic acid (LA) to γ‐valerolactone (GVL) is regarded as a critical process of the lignocellulose‐based biorefinery system. Substantial progress on the catalytic conversion of LA to GVL has been continuously achieved recently. However, the traditional research paradigm typically emphasizes the metal‐catalyzed hydrogenation step, but lacks profound insights into the potential impacts of catalyst supports. Herein, an overview of the bifunctional catalytic system classified by representative solid acid supports for LA conversion to GVL is presented, and effects of critical factors on metal‐ and acid‐ catalyzed processes are discussed. Particularly, impacts of key issues on catalytic stability are thoroughly summarized and analyzed. Challenges and suggestions are also proposed from the perspective of increases in both catalytic activity and stability. This review potentially contributes to the rational design of high‐efficiency catalysts used in the biomass valorization for renewable energy production.     

Ir‐Catalyzed Asymmetric Hydrogenation of α‐Alkylidene β‐Lactams and Cyclobutanones

Chiral β‐lactams and cyclobutanones are present in numerous natural and pharmaceutical products. The stereoselective construction of chiral four‐membered cyclic compounds is an ongoing challenge for the chemical community. Herein, we report a highly stereocontrolled construction of four‐membered ring (mini‐sized) β‐lactams and cyclobutanones via an Ir/ In‐BiphPHOX ‐catalyzed asymmetric hydrogenation, providing the corresponding optically active four‐membered ring carbonyl products bearing an α‐chiral carbon center with excellent yields (up to 99%) and enantioselectivities (up to 98%) under mild reaction conditions (1.0—2.5 bar H₂ for 1.0—10 h). The reaction presents wide substrate scope. Diverse transformations of the catalyzed products were also conducted to show the potential utility of this protocol.     

Insight into the Reaction Mechanism of α‐Amino Phosphonate Synthesis Using Succinic Acid as a Catalyst: Computational Kinetic Approach

The reaction mechanism in the synthesis of particular α‐amino phosphonates from 4‐methyl benzaldehyde, aniline, and trimethyl phosphite in the presence of succinic acid is theoretically investigated. The profile of the potential energy surface is constructed at both HF /6‐31 + G(d,p) and B3LYP /6‐31 + G(d,p) levels of theory for evaluating all the steps involved in the reaction mechanism. In order to investigate the effect of the structure on reactivity, some para ‐substituted benzaldehydes are subjected to kinetic examination. The overall reaction in the presence of electron‐withdrawing groups is thermodynamically much more favorable than in the presence of the electron‐donating groups; similarly, the reaction is kinetically more favorable and much easier in the presence of electron‐withdrawing groups. Moreover, step 2 (imine formation) is recognized as the rate‐determining step at both levels of theory. Also, step 1 is diffusion‐controlled with both electron‐withdrawing and electron‐donating groups, while the other steps are chemically controlled in the reaction mechanism.     

A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Synthesis of new optically active α,α′,β‐trisubstituted‐β‐lactones as monomers for stereoregular biopolyesters

Various optically active (4R)‐alkyloxycarbonyl‐3,3‐dialkyl‐2‐oxetanones as monomers were synthesized from L‐(S)‐malic acid in six steps to prepare a new family of stereopolyesters for biomedical applications. The synthesis began with an esterification followed of a dialkylation in the aim to introduce hydrophobic groups as methyl or reactive group as allyl. Then, a saponification has permitted to obtain the corresponding diacids that reacted with appropriate alcohols to furnish different monoesters. The last and most important step was activation of hydroxyl group of monoesters with the asymmetric carbon configuration inversion according to the Mitsunobu reaction. Thus, this reaction has provided lactones from monoesters with 100% enantiomeric excess which was confirmed by ¹H NMR and by the synthesis of corresponding isotactic and semicrystalline homopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2586–2597     

Studies on the Mass Spectra of N‐Aryl α,β‐Unsaturated γ‐Lactams

The mass spectra of a series of N‐aryl α,β‐unsaturated γ‐lactams were studied. Besides the molecular ion, the three characteristic fragments such as [M⁺‐29], [M⁺‐55], and [M⁺‐82] were commonly found in a series of N‐Aryl α,β‐unsaturated γ‐lactams in EI/MS. Further more the mechanism for the interpretation of these fragments is also de scribed.     

Aluminium Complexes Bearing Pyrrolide Ligand as Efficient Catalysts for Ring‐Opening Polymerization of ε‐Caprolactone

Three aluminium complexes supported by a tetradentate pyrrolide ligand H₂L [H₂L = N,N′‐(2,2‐dimethylpropane‐1,3‐diyl)bis(1‐(1H‐pyrrol‐2‐yl)methanimine)], namely, Al(L)Me ( 1 ), Al(L)Cl ( 2 ), and Al(L)(OiPr) ( 3 ), were synthesized. The structures of 1 and 2 were established by X‐ray single crystal diffraction analysis, and the structure of 3 was characterized by NMR spectroscopy and element analysis. All complexes, containing different chemical bond forms (Al–C, Al–Cl, and Al–O), are good initiators for the ring‐opening polymerization (ROP) of ε‐caprolactone. The obtained polymers have high molecular weights (MWs) and relatively narrow molecular weight distributions (PDIs). Complexes 1 and 3 show dramatically high activities for the ROP of ε‐caprolactone. For complex 1 , when the monomer/initiator (M/I) ratio is 6400:1, a 40 % yield of the product could be obtained at 100 °C. The activity of 3 is higher than that of 1 , and 39 % yield of the polymers could be afforded at 70 °C, as the M/I value reaches 12800:1. The good activities of these complexes reveal their potential applications in industry.     

Benzylamine as Hydrogen Transfer Agent: Cobalt‐Catalyzed Chemoselective C=C Bond Reduction of β‐Trifluoromethylated α,β‐Unsaturated Ketones via 1,5‐Hydrogen Transfer

An efficient cobalt‐catalyzed chemoselective reduction of β‐CF₃‐α,β‐unsaturated ketones using benzylamine as hydrogen transfer agent involving intramolecular 1,5‐hydrogen transfer is reported. The reaction proceeded smoothly with a relatively wide range of substrates including those bearing aromatic heterocycles such as a furyl ring system in high yields (74–92 %). This provides an efficient method for the synthesis of β‐CF₃ saturated ketones in one‐pot. This methodology was also applied to the selective C=C reduction of other enone substrates bearing no β‐CF₃‐substituent, of which β‐substituted or β,β‐disubstituted enones are tolerated, giving the desired products in good yields (72–75 %). Mechanistic studies indicate that the reaction involves 1,5‐hydrogen transfer.     

Chemical synthesis of poly‐γ‐glutamic acid by polycondensation of γ‐glutamic acid dimer: Synthesis and reaction of poly‐γ‐glutamic acid methyl ester

α‐Methyl glutamic acid (L ‐L )‐, (L ‐D )‐, (D ‐L )‐, and (D ‐D )‐γ‐dimers were synthesized from L ‐ and D ‐glutamic acids, and the obtained dimers were subjected to polycondensation with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and 1‐hydroxybenzotriazole hydrate as condensation reagents. Poly‐γ‐glutamic acid (γ‐PGA) methyl ester with the number‐average molecular weights of 5000∼20,000 were obtained by polycondensation in N,N‐dimethylformamide in 44∼91% yields. The polycondensation of (L ‐L )‐ and (D ‐D )‐dimers afforded the polymers with much larger |[α]_D | compared with the corresponding dimers. The polymer could be transformed into γ‐PGA by alkaline hydrolysis or transesterification into α‐benzyl ester followed by hydrogenation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 732–741, 2001     

Catalytic Hydrogenation of α,β-Epoxyketones to β-Hydroxyketones with Two Sulfinyl Analogues of Coenzyme NADH Models

An efficient method for the selective hydrogenation of a series of α,β-epoxyketones to β-hydroxyketones using catalytic amount of two sulfinyl analogues of NAD^＋ model compounds is reported. The lack of any diastereoselectivity for the formation of β-hydroxyketones with optically pure sulfinyl analogue of NAD^＋ model supports the radical mechanism proposed previously.     

The Efficient Synthesis of the Optically Active β‐Hydroxyl‐γ‐Butyrolactone Derivatives

The optically active β‐hydroxyl‐γ‐butyrolactones were synthesized from nonchiral starting material by employing reductive cleavage reaction, sharpless asymmetric epoxidation and dihydroxylation, and Lewis acid‐catalysed cyclization as key steps. This strategy can be used to prepare many chiral β‐hydroxyl‐γ‐butyrolactone analogues.     

The Renaissance of α‐Methylene‐γ‐butyrolactones: New Synthetic Approaches

The amount of research activity concerning α‐methylene‐γ‐butyrolactones and α‐alkylidene‐γ‐butyrolactones has increased dramatically in recent years. This Review summarizes the structural types, biological activities, and biosynthesis of these compounds, concentrating on publications from the past 10 years. Traditional approaches to α‐methylene‐γ‐butyrolactones and α‐alkylidene‐γ‐butyrolactones are then reviewed together with novel approaches, including those from our own research group, reported more recently.     

Synthesis of β‐Haloketones by β‐Addition Reactions of α,β‐Unsaturated Ketones with BX3 (X = Br,Cl) as Halide Source

A series of β‐bromoketones and β‐chloroketones were synthesized by the addition reactions of α,β‐unsaturated ketones under BX₃ (X = Br, Cl) and ethylene glycol reaction system. The α,β‐unsaturated ester also was successfully converted to its corresponding β‐bromoester under the reaction condition.