Ruthenium-catalyzed [2+2] cycloadditions between C1-substituted 7-oxanorbornadienes and alkynes

Ruthenium-catalyzed [2+2] cycloadditions between C1-substituted 7-oxanorbornadienes and alkynes were investigated. Most of the cycloadditions occurred smoothly at 65 °C, giving the cyclobutene cycloadducts in moderate to good yields. The C1 substituent showed strong effect on the regioselectivity (up to 110:1) of the cycloadditions.     

Reactivity of allenoates toward aziridines: [3+2] and formal [3+2] cycloadditions

The reactivity of buta-2,3-dienoates toward aziridines is reported. Allenoates react as 2π-component in the [3+2] cycloaddition with the azomethine ylide generated from cis-1-benzyl-2-benzoyl-3-phenylaziridine affording 4-methylenepyrrolidines in a site-, regio-, and stereoselective fashion. Under conventional thermolysis, cis- and trans-2-benzoyl-1-cyclohexyl-3-phenylaziridines showed a different reactivity. These aziridines participate in formal [3+2] cycloadditions with allenes via C-N bond cleavage of the three-membered ring leading to functionalized pyrroles.     

Palladium-catalyzed allylation and deacylative allylation of 3-acetyl-2-oxindoles with allylic alcohols

The Pd-catalyzed allylation of 3-acetyl-2-oxindoles with allyl alcohol is performed using 3 mol% of Pd(dba)₂, rac-BINAP and BINOL phosphoric acid as catalytic mixture. This procedure allows the in situ synthesis of 3-allyl-2-oxindole by adding Triton B to the reaction mixture. The deacylative allylation of 3-acetyl-3-methyl-2-oxindoles with allylic alcohols is carried out with 3 mol% of Pd(OAc)₂, dppp and 1.5 equiv. of LiOtBu as base affording the corresponding 3,3-disubstituted 2-oxindoles in good yields. Both methodologies can be combined for the preparation of unsymmetrical 3,3-diallylated 2-oxindoles such as compound 7. The DaA must be carried out in the absence of oxygen in order to avoid the competitive formation of 3-alkyl-3-hydroxy-2-indoles. The later compounds can be easily obtained by deacylative oxidation of 3-alkylated 3-acetyl-2-oxindoles with LiOEt at rt under air.     

Palladium-catalyzed asymmetric synthesis of allylic alcohols from unsymmetrical and symmetrical racemic allylic carbonates featuring C-O-bond formation and dynamic kinetic resolution

Described is the asymmetric synthesis of the allylic alcohols 11 (85% ee), 15 (99% ee), 17 (93% ee), 19 (61% ee), and 21 (69% ee) through a Pd-catalyzed reaction of the unsymmetrical carbonates rac-10, rac-12, rac-14, rac-16, rac-18, and rac-20, respectively, with KHCO₃ and H₂O in the presence of bisphosphane 6. Similarly the allylic alcohols 23 (99% ee) and 25 (97% ee) have been obtained from the symmetrical carbonates rac-22 and rac-24, respectively. Reaction of the meso-biscarbonate 26 with H₂O and Pd(0)/6 afforded alcohol 27 (96% ee), which was converted to the PG building block 32. The unsaturated bisphosphane 33 showed in the synthesis of alcohols 36, 37, and 39 a similar high selectivity as 6. The formation of alcohols 11, 15, and 17 involves an efficient dynamic kinetic resolution.     

Palladium-catalyzed concerted [4 + 1] cyclization of prop-2-yn-1-ones and isocyanides

A palladium-catalyzed [4+1] cycloaddition of prop-2-yn-1-ones with double isocyanides is developed herein.The transformation worked well to produce a series of 2-amino-4-cyanofurans with high efficiency and a broad reaction scope.Based on mechanism studies,it is believed that the palladiumcatalyzed [4+1] imidoylative cycloaddition of prop-2-yn-1-ones was concerted.Treated with a ryl amine and H_2 O,the [4+1] cycloaddition of prop-2-yn-1-ones with double isocyanides provided 2-amino-4-amidylpyrroles efficiently.     

Palladium-Catalyzed [6+2] Double Allene Annulation for Benzazocines Synthesis

An efficient double allene protocol for the formation of benzazocines has been developed. The reaction constitutes a highly regioselective palladium-catalyzed formal [6+2] annulation of allenyl benzoxazinanones with terminal allenes forming the challenging 8-membered cycles. Decent yields and excellent regioselectivity have been observed under mild conditions with a remarkable Z-stereoselectivity for the exo-cyclic C=C bonds. The synthetic potentials of benzazocine products have been demonstrated.     

Synthesis of psudoheliotridane via formal [3+2] annulation and ring-closing metathesis

Base-induced coupling/cyclization stepwise [3+2] annulation of α-sulfonylacetamide with (Z)-2-bromoacrylates yielded polysubstituted pyroglutamates with three contiguous chiral centers with trans-trans orientation in a one-pot synthesis. The pyrrolizidine skeleton was obtained via the ring-closing metathesis (RCM) method. This facile strategy was used to synthesize psudoheliotridane.     

Phosphine-catalyzed enantioselective [3+2] annulations of 2,3-butadienoates with imines

The first systematic screening of chiral phosphines in the cycloaddition reaction between 2,3-butadienoates and arylimines has led to the identification of fairly efficient catalysts. 2-Aryl-3-pyrrolines have been obtained with enantiomeric excesses up to 64%. In one instance, the enantiomeric excess could be increased to 91% ee by combining the enantioselective cyclization reaction with a crystallization step.     

Reaction of ene-bis(phosphinylallenes): [2+2] versus [4+2] cycloaddition

Reaction of ene-bis(phosphinylallenes), derived from ene-bis(propargyl alcohols) and chlorodiphenylphosphine, was investigated. Benzene-bridged bis(phosphinylallenes) exclusively gave intramolecular [2+2] cycloadducts in the presence of dimethyl fumarate in sharp contrast to the reaction of benzene-bridged bis(sulfinylallenes), which gave the corresponding [4+2] cycloadducts. On the other hand, substituted ethylene- or five-membered heterocycle-bridged bis(phosphinylallenes) provided [4+2] cycloadducts. Reaction of benzene-bridged diallene bearing both a sulfinyl group and a phosphinyl group on the two allenyl groups was also described.     

Novel formal [2+3] cycloaddition between substituted phenols and furan

Treatment of various substituted phenols in the presence of furan, iodobenzene diacetate, and trifluoroethanol promotes oxidative formal [2+3] cycloaddition in moderate to useful yields.     

Organocatalytic Formal Intramolecular [3+2]-Cycloaddition to Acquire Biologically Important Methanodibenzo[a,f]azulenes and Methanobenzo[f]azulenes

Lawsones were transformed into the functionally rich framework of methanodibenzo[a,f]azulenes and methanobenzo[f]azulenes in a single- or two-pot operation through five organocatalytic sequential reactions in very good yields with excellent selectivities. These resultant molecules are basic skeletons of important antibiotics, which highlights the value of this formal intramolecular [3+2]-cycloaddition as a key protocol.     

Synthesis of conformationally restricted nicotine analogues by intramolecular [3+2] cycloaddition

We describe the synthesis of a series of conformationally constrained nicotine analogues 2-5 from appropriate pyridine-containing enals, featuring an intramolecular azomethine ylide-alkene [3+2] cycloaddition. The objective of the current project is to develop new selective nAChRs-targeting ligands. Of the nicotine analogues that we have studied, the conformation-restricting ring B unit can be either a five-membered carbocycle, or a six-membered carbocycle or heterocycle. The present work constitutes a general method for rapid assembly of other related tricyclic nicotine analogues.     

Silver Catalyzed Decarbonylative [3 + 2] Cycloaddition of Cyclobutenediones and Formamides

As an important moiety in natural products, N,O-acetal has attracted wide attention in the past few years. An efficient method to construct N,O-acetal has been developed. Using silver catalyst, cyclobutenediones were smoothly converted to the corresponding γ-aminobutenolides in the presence of formamides, in which cyclobutenediones likely proceed with a key decarbonylative [3 + 2] cycloaddition process. In this way, a series of products with varied substituents were isolated in moderate yield and fully characterized.     

Highly efficient and regioselective allylic amination of allylic alcohols catalyzed by [Mo3PdS4] cluster

A highly efficient and regioselective allylation reaction of amines with allylic alcohols under mild conditions catalyzed by the cubane-type sulfido cluster [(Cp∗Mo)₃S₄Pd(dba)][PF₆] with H₃BO₃ as an additive has been developed. A variety of amines and allylic alcohols are investigated, and in the case of allylic alcohols bearing substituents at either α- or γ-position only linear allylic amination products are obtained.     

Scope of the formal [3+2] cycloaddition for the synthesis of substituted 3-arylindanes and related compounds

We report the single step synthesis of several 3-arylindanes and related compounds via a formal [3+2] cycloaddition. A study of the influence of the aromatic ring substitution pattern on the reaction was carried out.     

纳米银粒子对[Ru(bpy)_3]~(2+)光谱学性质的影响及电解质效应

研究了[Ru(bpy)3]2+溶液中引入纳米银粒子的光谱学性质变化规律以及[Ru(bpy)3]2+与纳米银粒子所构成的溶液体系([Ru(bpy)3]2+-Ag)的电解质效应.研究结果表明,[Ru(bpy)3]2+吸附在纳米银粒子表面使纳米银粒子相互桥连形成规则的类链状网络聚集体.纳米银粒子造成[Ru(bpy)3]2+溶液荧光猝灭,且大尺寸的纳米银粒子引起的荧光猝灭程度较大.在[Ru(bpy)3]2+-Ag体系中引入电解质造成纳米银粒子不同程度的聚集和生长.电解质对纳米银聚集影响为:CaCl2MgCl2Ca(NO3)2KClKNO3.随着[Ru(bpy)3]2+-Ag体系中引入电解质含量的增加,溶液的荧光强度先降低而后又逐渐增强,直至达到定值,表明一定量的电解质可产生荧光猝灭释放效应.电解质对荧光强度影响顺序为:Ca(NO3)2CaCl2MgCl2KClKNO3.采用透射电子显微镜、紫外-可见吸收分光光度计和荧光分光光度计等手段从分子间相互作用和能量传输等方面初步探讨了纳米银粒子对表面吸附[Ru(bpy)3]2+溶液光谱学性质的影响机制以及电解质效应.     

Synthesis of 2-azaspiro[4.4]nonan-1-ones via phosphine-catalysed [3+2]-cycloadditions

The phosphine-catalyzed [3+2]-cycloaddition of the 2-methylene γ-lactams 4 and 5 and the acrylate 6 with the ylides derived from the ethyl ester, the amide or the chiral camphor sultam derivative of 2-butynoic acid (7a-c) give directly, or indirectly after reductive cyclization, spiro-heterocyclic products. The acid 32 underwent Curtius rearrangement and then acid hydrolysis to give two novel spiro-cyclic ketones, 41 and 42.     

Lewis acid-mediated [3+2] cycloaddition between hydrazones and olefins

[3+2] Cycloaddition between hydrazones and olefins was accelerated in the presence of a stoichiometric amount of BF₃·OEt₂ or a catalytic amount of Zr(OTf)₄, Hf(OTf)₄, or Sc(OTf)₃ under mild conditions. The corresponding pyrazolidine derivatives were obtained in moderate to high yields using this novel [3+2] Lewis acid catalysis.     

Thiourea-catalyzed asymmetric formal [3+2] cycloaddition of azomethine ylides with nitroolefins

A chiral thiourea catalyst possessing an amine function catalyzes an asymmetric [3+2] cycloaddition of azomethine ylides to nitroolefins to provide highly functionalized pyrrolidines with high diastereo- and enantioselectivities (up to 98:1:1 dr, 92% ee). The reaction proceeds in a stepwise manner consisting of Michael addition and subsequent intramolecular aza-Henry reaction. Both reactions are promoted by the thiourea catalyst, and the reaction rate of the latter step is efficiently enhanced by the addition of 2,2,2-trifluoroethanol.