Enantioselective Allylic Amination of Morita‐Baylis‐Hillman Acetates Catalyzed by Chiral Thiourea‐Phosphine

The enantioselective allylic amination of Morita‐Baylis‐Hillman acetates catalyzed by chiral cyclohexane‐based thiourea‐phosphine catalysts was investigated. In the presence of 20 mol% rosin‐derived thiourea‐phosphine 3j , the chiral amines were obtained in up to 88% yield and up to 85% ee.     

Highly Enantioselective Intramolecular Morita‐Baylis‐Hillman Reaction Catalyzed by Mannose‐Based Thiourea‐phosphine

The saccharide‐based chiral bifunctional thiourea‐phosphines were developed as chiral organocatalysts for the intramolecular Morita‐Baylis‐Hillman reaction of ω‐formyl‐enones. With only 2 mol% of thiourea‐phosphine catalyst 3c , chiral functionalized cyclohexenes were achieved under mild reaction conditions with excellent yields and enantioselectivities.     

Rate Acceleration of the Baylis‐Hillman Reaction within Microreactors

Based on microreactors, the representative Baylis‐Hillman reaction of cyclopent‐2‐enone coupled with 4‐nitrobenzaldehyde in the presence of imidazole could be accelerated by manipulating the temperature and electric field. Furthermore, the electric field was used in promoting Baylis‐Hillman reaction for the first time with the rate acceleration approximately 5.2‐fold higher than that carried out in conventional vessels as well as 4.0‐fold under control of temperature. Meanwhile, the products of Baylis‐Hillman reaction at every time point could be collected and then determined by capillary micellar electrokinetic chromatography.     

Asymmetric Baylis–Hillman Reactions Promoted by Chiral Imidazolines

The coupling of electrophiles with activated alkenes by using tertiary amines or phosphines is generally known as the Baylis–Hillman reaction. It is a useful and atom‐economical carbon–carbon bond‐forming reaction that generates multifunctionalized products. This reaction is notoriously slow; yields are often low and substrate‐dependent. The asymmetric reaction is still limited especially for unactivated olefins such as acrylates. Imidazolines have been developed as ligands in metal‐catalyzed reactions and have also been used as privileged structures in diversity‐oriented synthesis. A series of novel chiral imidazolines were prepared and used to develop asymmetric Baylis–Hillman reactions. These imidazolines promote the reactions of various aromatic aldehydes with unactivated acrylates. Enantiomeric excesses of up to 60 % and high yields were obtained by using stoichiometric amounts of the promoter. Furthermore, the imidazolines are also suitable promoters for the reactions between aromatic aldehydes and alkyl vinyl ketones. Enantiomeric excesses of up to 78 % and high yields were obtained with 50 mol % of an imidazoline with a chiral methylnaphthyl group. These chiral imidazolines are easily prepared from commercially available amino alcohols and can be easily recovered for reuse without loss of product enantioselectivity.     

从Baylis-Hillman溴化物方便的合成N-取代的咪唑和苯并三氮唑

在室温下, 通过Baylis-Hillman溴化物与咪唑或苯并三氮唑反应, 方便的合成了N-取代的咪唑和苯并三氮唑衍生物. 该方法的优点为操作简单, 反应条件温和, 产率高, 好的区域和立体选择性.     

α‐ZrP/Uracil/Cu2+ nanoparticles as an efficient catalyst in the Morita‐Baylis‐Hillman reaction

A facile synthesis of uracil‐Cu²⁺ nanoparticles immobilized on alpha‐zirconium hydrogen phosphate (α‐ZrP), abbreviated as α‐ZrP/Uracil/Cu²⁺, was presented. This compound was synthesized by the thermal method and used as a reusable catalyst for the Morita‐Baylis‐Hillman reaction without any additives. First, (3‐ iodopropyl) trimethoxysilane as a linker is reacted with α‐ZrP support to give the α‐ZrP/IPTMOS. Addition of uracil and then the addition of copper (II) acetate to α‐ZrP/IPTMOS results in the production of selected catalyst. The Morita‐Baylis‐Hillman reaction catalyzed by α‐ZrP/Uracil/Cu^{2 +} demonstrated high product yield, short reaction time and a straightforward work‐up. The catalyst with enough outside surface was easily recovered using centrifugation and reused five times without a significant reduction in its activity.     

Density Functional Study of Proline‐Catalyzed Intramolecular Baylis–Hillman Reactions

A rationalization of stereoselectivity : The mechanisms of proline‐catalyzed and imidazole‐co‐catalyzed intramolecular Baylis–Hillman reactions have been studied by using density functional theory methods. The computational data has allowed us to rationalize the experimental outcome, validating some of the mechanistic steps proposed in the literature, as well as to propose new ones that considerably change and improve our understanding of the full reaction path (see scheme).

     

Boron（Ⅲ） Tribromide or Tianium （Ⅳ） Bromide and Lewis Base Promoted Baylis—Hillman Reaction

It was found that,when the Baylis-Hillman reaction of arylaldehydes with methyl vinyl ketone was carried out at below -20℃ in the presence of boron (Ⅲ） tribromide or titanium (Ⅳ） bromide using a catalytic amount of Lewis base such as amine,the brominated compounds and the Baylis-Hillman adducts could be obtained as the major products in good yields for various aryl aldehydes.But at room temperature,the elimination products were the major products.In addition,the palladium catalyzed allylic substitution reactions of the elimination products were also examined.     

An Efficient and Practical Synthesis of Dibenzo[d,f][1,3]‐dioxepines from 2,2′‐Dihydroxybiphenyl with Terminal Alkynes Catalyzed by Lewis Acid TiCl4

A synthetic strategy toward the cyclic addition of 2,2′‐dihydroxybiphenyl to terminal alkynes has been developed using Lewis acid TiCl₄ as catalyst. The reactions generated dibenzo[d,f][1,3]dioxepines derivatives in good yields with excellent regio‐selectivity in the presence of catalytic amount of TiCl₄ under mild reaction conditions.     

A Rapid and Efficient Stereoselective Synthesis of (Z)‐ and (E)‐Allyl Bromides from Baylis–Hillman Adducts Using Bromo(dimethyl)sulfonium Bromide

Treatment of Baylis–Hillman adducts 1 with bromo(dimethyl)sulfonium bromide, Br(Me₂)S⁺Br^?, in MeCN was found to stereoselectively afford (Z)‐ and (E)‐allyl bromides 2 . The reaction is rapid at room temperature, high‐yielding, and highly stereoselective.     

从Baylis-Hillman加成物合成1，2，3，4-四氢苯并萘啶-2-酮衍生物

本文介绍了（2）通过还原、两次环化的一锅串联反应制备了一系列1,2,3,4-四氢苯并萘啶-2-酮衍生物,反应条件温和,环境友好,产品易于分离,反应收率中等。起始原料可由Baylis－Hillman加成物通过Johnson-Claisen重排制备。     

Brønsted Acid Catalyzed Morita–Baylis–Hillman Reaction: A New Mechanistic View for Thioureas Revealed by ESI‐MS(/MS) Monitoring and DFT Calculations

A Morita–Baylis–Hillman (MBH) reaction catalyzed by thiourea was monitored by ESI‐MS(/MS) and key intermediates were intercepted and characterized. These intermediates suggest that thiourea acts as an organocatalyst in all steps of the MBH reaction cycle, including the rate‐limiting proton‐transfer step. DFT calculations, performed for a model MBH reaction between formaldehyde and acrolein with trimethylamine as base and in the presence or the absence of thiourea, suggest that thiourea accelerates MBH reactions by decreasing the transition‐state (TS) energies through bidentate hydrogen bonding throughout the whole catalytic cycle. In the rate‐limiting proton‐transfer step, the thiourea acts not as a proton shuttle, but as a Brønsted acid stabilizing the basic oxygen center that is formed in the TS.