Synthesis of Bridged Cyclopentane Derivatives by Catalytic Decarbonylative Cycloaddition of Cyclobutanones and Olefins

Herein, we report an intramolecular rhodium‐catalyzed decarbonylative coupling between cyclobutanones and alkenes that proceeds by C?C activation and provides a distinct approach to a diverse range of saturated bridged cyclopentane derivatives. In this reaction, cyclobutanones serve as cyclopropane surrogates, reacting in a formal (4+2?1) transformation. To demonstrate the efficacy of this method, it was applied in a concise synthesis of the antifungal drug Tolciclate.     

1,3-Dipolar Cycloaddition of Dipolar Reagents to Bifunctional Olefins with Chloramine-T --- Part-II

A one pot synthesis of pyrazoles and isoxazoles was achieved by 1,3-dipolar cycloaddition of nitrile imines and nitrile oxides to an activated olefins in the presence of chloramine-T.     

Studies on the Intermolecular Cycloaddition of Diphenylacetonitrile Oxide with Substituted Olefins

We present our findings on the regio- and stereo chemical outcome of the cycloadditions of sterically crowded diphenylacetonitrile oxide towards mono and disubstituted electron deficient and electron rich olefins. The resultant Δ²-isoxazolines are further transformed to their corresponding β-hydroxy carbonyl compounds employing Curran's protocol.     

Photocycloaddition Reactions of Pyrazinopsoralen with Simple Olefins

Direct photolyses of pyrazinopsoralen (PzPs) with excess olefins such as dimethyl fumarate (DMFu), dimethyl maleate (DMMa) and dimethyl ethylidenemalonate (DMEM) gave C₄-photocycloadducts. The photoproducts were determined to be 1:1 C₄-cycloadducts formed through the addition of 4',5'-furan double bond of the excited P_zP_s to the olefins. The fluorescence of P_zP_s was quenched by olefins with rate constants on the order of 10₉–10₁₀ M -¹/s. The appearance of the long-lived fluorescence component implies a singlet exciplex mechanism for the photocycloaddition reaction of PzPs with excess olefins.     

Rhodium-Catalyzed Regio- and Diastereoselective [3+2] Cycloaddition of gem-Difluorinated Cyclopropanes with Internal Olefins

Direct synthesis of gem-difluorinated carbocyclic molecules represents a longstanding challenge in organic chemistry. Herein, a Rh-catalyzed [3+2] cycloaddition reaction between readily available gem-difluorinated cyclopropanes (gem-DFCPs) and internal olefins has been developed, enabling the efficient synthesis of gem-difluorinated cyclopentanes with good functional group compatibility, excellent regioselectivity and good diastereoselectivity. The resulting gem-difluorinated products can undergo downstream transformations to access various mono-fluorinated cyclopentenes and cyclopentanes. This reaction demonstrates the use of gem-DFCPs as a type of “CF₂” C3 synthon for cycloaddition under transition metal catalysis, which provides potential strategy for synthesizing other gem-difluorinated carbocyclic molecules.     

1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Schiff Bases and Difluorocarbene to Symmetric Olefins

Difluoro(iminio)methanides generated by the action of difluorocarbene on Schiff bases react with derivatives of maleic and fumaric acids, following the 1,3-dipolar cycloaddition pattern to give 2,2-difluoropyrrolidines which were detected by gas chromatography-mass spectrometry. The final products are stereo-isomeric substituted 2-pyrrolidinones formed by hydrolysis of difluoropyrrolidines and their dehydrofluorination products, 2-fluoro-4,5-dihydropyrroles. The observed stereoselectivity of the cycloaddition suggests Z configuration of intermediate ylide and both endo- and exo-approach to the dipolarophile in the transition state corresponding to cycloaddition.     

1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Ketimines and Difluorocarbene to Symmetrically Substituted Olefins

Iminiodifluoromethanides generated from difluorocarbene and benzophenone or fluorenone imines enter into reaction of 1,3-cycloaddition with electron-deficient alkenes to furnish pyrrolidone derivatives. The generation of iminiodifluoromethanides from alkyl N-benzhydrylidene glycinates in the presence of dipolarophiles is liable to complication by a concurrent proton shift in the initial imine giving NH-azomethine ylide also capable of 1,3-dipolar cycloaddition resulting in a side product of pyrrolidone series. The use of active lead instead of lead powder as reductant for dibromodifluoromethane in generation of difluorocarbene permits suppressing formation of the side products in these reactions.     

Cycloaddition of CO2 to epoxides catalyzed by polyaniline salts

The catalytic activity of polyaniline-HX (X=I, Br, Cl) (PANI-HI, PANI-HBr, PANI-HCl) for the cycloaddition of CO2 to propylene oxide (PO) to produce propylene carbonate (PC) was studied for the first time. It was shown that all the PANI salts were active for the reaction, and PANI-HI was most active and selective. On the basis of the preliminary results, the effect of the reaction conditions on the cycloadditions of CO2 to propylene oxide and epichlorohydrin was further investigated by using PANI-HI as the catalyst. The results indicated that the optimized temperature was around 115 degrees C. The maxima occurred in yield versus pressure curves at about 5 MPa for both substrates. Complete conversion was achieved in 3 h for epichlorohydrin and 6 h for propylene oxide at 115 degrees C and 5 MPa. With propylene oxide as the substrate, the reusability of PANI-HI was evaluated and no loss of catalytic activity was detectable after the catalyst had been reused five times. The catalyst was characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), which provided further evidence for the high stability of the catalyst. We believe that the catalyst has great potential for industrial applications because it has some unusual advantages, such as its easy preparation, high activity, selectivity, stability, low cost, and simple separation from products.     

Divergent Photosensitizer Controlled Reactions of 4-Hydroxycoumarins and Unactivated Olefins: Hydroarylation and Subsequent [2+2] Cycloaddition

Herein, we report a photoinduced approach for hydroarylation of unactivated olefins using 4-hydroxycoumarins as the arylating reagent. Key to the success of this reaction is the conversion of nucleophilic 4-hydroxycoumarins into electrophilic carbon radicals via photocatalytic arene oxidation, which not only circumvents the polarity-mismatch issue encountered under ionic conditions but also accommodates a broad substrate scope and inhibits side reactions that were previously observed. Moreover, divergent reactivity was achieved by changing the photocatalyst, enabling a subsequent [2+2] cycloaddition to deliver cyclobutane-fused pentacyclic products that are otherwise challenging to access in high yields and with high diastereoselectivity. Mechanistic studies have elucidated the mechanism of the reactions and the origin of the divergent reactivity.     

酮-过氧化氢体系对烯烃的环氧化

过氧化酮是优良的烯烃环氧化试剂,可将烯烃氧化成环氧化物。在这些反应中,所用的氧化剂都是过硫酸氢钾或商品Oxone^[1-6]。用其它氧化剂与酮生成过氧化酮使烯烃环氧化的报道很少^[7,8],只有一例是使用过氧化氢作氧化剂的,但其只研究了一种酮与过氧化氢对烯烃的环氧化^[8]。本文使用价格便宜,且没有污染的过氧化氢取代Oxone,与酮反应形成的过氧化酮使烯烃环氧化,并首次研究了一系列酮化合物与过氧化氢组成的催化体系对烯烃的环氧化反应,考察了各种酮的催化活性。     

Cycloaddition of 2-pyridinetellurenyl chloride to alkenes

The action of 2-pyridinetellurenyl chloride on alkenes results in the polar cycloaddition of the tellurium-centered electrophile at the multiple bond with the formation of 2,3-dihydro[1,3]tellurazolo[3,2-a]pyridinium derivatives.