[2+2+1+1] Cycloaddition for de novo Synthesis of Densely Functionalized Phenols

A unique benzannulation strategy for regioselective de novo synthesis of densely functionalized phenols is described. Through metal-mediated formal [2+2+1+1] cycloaddition of two different alkynes and two molecules of CO, a series of densely functionalized phenols were obtained. The benzannulation strategy allows efficient regioselective installation up to five different substituents on a phenol ring. The resulting phenols have a substitution pattern different from those obtained from Dötz and Danheiser benzannulations.     

Rhodium-catalyzed [2+2+1+1] cyclocarbonylative coupling of alkynes with carbon monoxide affording tetrasubstituted p-benzoquinones

In this strategy, the tetrasubstituted benzoquinones have been prepared directly by a [2+2+1+1] cyclocarbonylative coupling reaction of internal alkynes with CO in the presence of [RhCl(CO)2]2. The low concentration of CO in the reaction is the crucial point for the chemoselective formation of tetrasubstituted benzoquinones in good to high yields. Functional groups such as chloro, methoxy, cyano, vinyl, fluoro, and carboxylate are tolerated under the reaction conditions.     

Recent advances in radical-mediated [2+2+m] annulation of 1,n-enynes

1,n-Enynes are a versatile class of unsaturated hydrocarbons that found broad applications in the synthetic community of natural products, biologically active structures and functional materials. Typical methods for the transformations of 1,n-enynes include the radical-mediated [2+2+m] annulation reaction as they are particularly efficient accesses to functionalized polycyclic compounds. We herein highlighted recent process in the radical-mediated [2+2+m] annulation of 1,n-enynes, including [2+2+1] and[2+2+2] modes, for the construction of five-to six-membered-ring-fused polycyclic scaffolds. Meanwhile, the mechanisms for these transformations were described.     

Novel [2 + 2 + 2 + 1] cycloaddition of enediynes catalyzed by rhodium complexes

[reaction: see text] The first Rh-catalyzed intramolecular [2 + 2 + 2 + 1] cycloaddition reaction of enediynes and CO is reported. This novel higher order cycloaddition process gives the corresponding 5-7-5 ring systems in high yield and selectivity. This process is another significant addition to the arsenal of cycloaddition-based synthetic methods, which provide powerful tools for rapid and efficient construction of complex polycyclic systems.     

Development of Gold‐catalyzed [4+1] and [2+2+1]/[4+2] Annulations between Propiolate Derivatives and Isoxazoles

Two new gold‐catalyzed annulations of isoxazoles with propiolates have been developed. Most isoxazoles follow an initial O attack on the alkyne to afford a [4+1] annulation product. This process results in a remarkable alkyne cleavage of initial propiolates. Unsubstituted isoxazoles proceed through an N attack step to yield formal [2+2+1]/[4+2] annulation products. These two annulation products arise initially from two seven‐membered heterocyclic intermediates, which then lead to products.     

Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage

It has been established that an electron-deficient cyclopentadienyl rhodium(III) (Cp^ERh^III) complex catalyzes the oxidative and decarboxylative [2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the Cp^ERh^III complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding [2+1+2+1] cycloaddition product. The synthetic utility of the present [2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor [5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction.     

Multicomponent cycloadditions: the four-component [5+1+2+1] cycloaddition of vinylcyclopropanes, alkynes, and CO

Prompted by the view that intermediates of transition metal-catalyzed reactions could be intercepted by one or more additional components, studies in our laboratory have led to the design and development of new three-component [5+2+1], [4+2+1], and [2+2+1] cycloadditions. These continuing studies have now led to the identification of a fundamentally new four-component [5+1+2+1] cycloaddition reaction of vinylcyclopropanes, alkynes and CO, yielding hydroxyindanone products in generally good yields. Terminal alkynes bearing aryl or alkyl groups are tolerated well. Substitution at any position of the VCP leads predictably to substituted hydroxyindanone products. Using a bis-alkynyl substrate, the reaction can be carried out bi-directionally, forming 10 C-C bonds and four new rings from seven components in a single, operationally simple process.     

Enantioselective sensing of amines based on [1 + 1]-, [2 + 2]-, and [1 + 2]-condensation with fluxional arylacetylene-derived dialdehydes

Four induced circular dichroism (ICD) probes exhibiting a stereodynamic arylacetylene framework and terminal aldehyde units have been prepared. The CD silent sensors generate a strong chiroptical response to substrate-controlled induction of axial chirality upon selective [1 + 1]-, [2 + 2]-, and [1 + 2]-condensation. The intense Cotton effects can be exploited for in situ ICD analysis of the absolute configuration and ee of a wide range of amines.     

Phosphole-Fused Dehydropurpurins via Titanium-Mediated [2+2+1] Cyclization Strategy

A [2+2+1] cyclization strategy of bis(alkynyl)porphyrin using low-valent titanium species, generated in situ, afforded phosphole-fused dehydropurpurins for the first time. The systematic investigations on the electronic properties of the dehydropurpurins revealed their unique features owing to the oxidation states of the phosphorus atom on the fused phosphole ring. The phosphole P=O and P=S derivatives were found to possess high electron-accepting character derived from phosphorus(V) centers without the contribution of 24π antiaromatic character, suggesting their potential utility as electron-accepting materials. In contrast, the phosphorus(III) derivatives revealed different optical and electrochemical properties arising from both 18π aromatic and 24π antiaromatic networks including the lone pair of the phosphorus(III) atom. Overall, the oxidation state of the phosphorus atom has a clear impact on the whole electronic properties, demonstrating the advantages of chemical modifications of the phosphorus center for creating an exotic π-system. The application of titanium-mediated [2+2+1] cyclization to porphyrins is highly promising for expanding a world of heterole-fused porphyrinoids.     

Unusual S-shaped binodal curves of the systems water+lithium chloride+1-butanol or 2-butanol or 2-methyl-1-propanol

Solid–liquid–liquid equilibrium data of the ternary systems water+LiCl+2-butanol, water+LiCl+2-methyl-1-propanol (i-butanol) and water+LiCl+1-butanol have been experimentally determined at 25°C. The equilibrium diagrams determined show differences between the systems. In the system with 1-butanol, the solid phase of the liquid–liquid–solid region is monohydrated salt. However, in the systems with 2-butanol and 2-methyl-1-propanol it is anhydrous salt. With respect to the liquid+liquid zone, the three diagrams are very similar with an unusual S-shaped solubility curve in the organic branch that can be explained depending on whether the organic solvent takes part in the solvation of ions. The more salt, the more numbers of ions solvated by water and organic solvent and the solubility of water and salt in the organic phase increase notably producing the unusual S-shaped solubility curve.     

Silicon-initiated carbonylative carbotricyclization and [2+2+2+1] cycloaddition of enediynes catalyzed by rhodium complexes

The reaction of dodec-11-ene-1,6-diynes or their heteroatom congeners with a hydrosilane catalyzed by Rh(acac)(CO)2 at ambient temperature and pressure of CO gives the corresponding fused 5-7-5 tricyclic products, 5-oxo-1,3a,4,5,7,9-hexahydro-3H-cyclopenta[e]azulenes or their heteroatom congeners, in excellent yields through a unique silicon-initiated cascade carbonylative carbotricyclization (CO-SiCaT) process. It has also been found that the 5-7-5 fused tricyclic products can be obtained from the same type of enediynes and CO through a novel intramolecular [2+2+2+1] cycloaddition process. The characteristics of these two tricyclization processes and the fundamental differences in their reaction mechanisms are discussed. This novel higher-order cycloaddition reaction has also been successfully applied to the tricyclization of undeca-5,10-diyn-1-als, affording the corresponding 5-7-5 fused-ring products bearing a seven-membered lactone moiety. Related [2+2+2] tricyclizations of enediyne and diynal substrates are also discussed. These newly discovered reactions can construct multiple bonds all at once, converting linear starting materials to polycyclic compounds in a single step. Thus, these new processes provide innovative routes to functionalized polycyclic compounds that are useful for the syntheses of natural and unnatural products.     

Cs1-xSn1-xBi9+Se15 and Cs1.5-3xBi9.5+xSe15: members of the homologous superseries Am[M1+lSe2+l]2m[M1 + 2l+nSe3 + 3l+n] (A = alkali metal,M = Sn and Bi) allowing structural evolution in three different dimensions

Cs1-xSn1-xBi9+xSe15 and Cs1.5-3xBi9.5+xSe15 crystallize in a new structure type which does not belong to but is closely related to the members of the homologous series Am[M6-Se8]m[M5+nSe9+n]; the new phases reveal a third dimension of structural evolution for this series according to the formula Am[M1+lSe2+l]2m[M1 + 2l + nSe3 + 3l+n].     

Electronic spectra of linear isoelectronic clusters C2n+1S and C2n+1Cl+ (n = 0-4): an ab initio study

Structures and stabilities of linear carbon chains C2n+1S and C2n+1Cl+ (n=0-4) in their ground states have been investigated by the CCSD and B3LYP approaches. The CASSCF calculations have been used to determine geometries of selected excited states of both isoelectronic series. Linear C2n+1S cluster has a cumulenic carbon framework, whereas its isoelectronic C2n+1Cl+ has a dominant character of acetylenic structure in the vicinity of terminal Cl. The vertical excitation energies of low-lying excited states have been calculated by the CASPT2 method. Calculations show that the excitation energies have nonlinear size dependence. The 2(1)Sigma+<--X1Sigma+ transition energy in C2n+1S has a limit of 1.78 eV, as the chain size is long enough. The predicted vertical excitation energies for relatively strong 1(1)Pi<--X1Sigma+ and 2(1)Sigma+<--X1Sigma+ transitions are in reasonable agreement with available experimental values. The spin-orbit effect on the spin-forbidden transition in both series is generally small, and the enhancement of the spin-forbidden transition by spin-orbit coupling exhibits geometrical and electronic structural dependence.     

Theoretical study of the [2+2+2+1] cycloaddition mechanism of enediynes and carbon monoxide catalyzed by rhodium

The [2+2+2+1] cycloaddition mechanism of enediynes and carbon monoxide catalyzed by the [Rh(CO)2Cl]2 rhodium dimer has been studied using density functional theory, comparing this multistep process with the two-step reaction in the absence of a catalyst. According to our results, the multistep mechanism agrees with that previously suggested. The great selectivity of this reaction and the influence of the chosen solvent in this selectivity were also analyzed.     

Efficient [4+1]/[3+2+1] bis-cyclizations stereoselectively yielding unprecedented polyacyclic indeno-fused xanthenes

Concise and efficient [4+1]/[3+2+1] bis-cyclizations of o-phthalaldehyde with cyclic 1,3-dicarbonyls have been established for the stereoselective synthesis of unprecedented polycyclic indeno[2,1-l]xanthene derivatives. The multicomponent domino reaction (MDR, AB₂ type) is easy to perform by mixing inexpensive substrates in HOAc at room temperature. The present synthesis shows attractive properties such as the simple one-pot fashion, high bond-forming efficiency, and easy purifications. Up to two new rings and four sigma-bonds were achieved in these MDRs without using any metal catalysts.     

Phosphine-catalyzed cascade [3 + 2] cyclization-allylic alkylation, [2 + 2 + 1] annulation, and [3 + 2] cyclization reactions between allylic carbonates and enones

The phosphine-catalyzed annulations between Morita-Baylis-Hillman adduct carbonates and enones are reported. Under the catalysis of PBu(3) (20 mol %), cascade [3 + 2] cyclization-allylic alkylation, [2 + 2 + 1] annulation, and [3 + 2] cyclization reactions chemoselectively occur depending on the substituent variation of both the carbonate and enone. These reactions provide efficient syntheses of highly functionalized cyclopentenes and cyclopentanes.     

A new Co(2)(CO8-mediated tandem [5 + 1]/[2 + 2 + 1]-cycloaddition reaction: a one-pot synthesis of tricyclic delta-lactones from cis-epoxy ene-ynes

In the presence of Co2(CO)8 and CO, cis-epoxyalkynes bearing a tether olefin undergo a tandem [5 + 1]/[2 + 2 + 1]-cycloaddition to give tricyclic delta-lactones efficiently in a one-pot operation. The reaction mechanism is proposed to involve a cobalt-coordinated cyclic allene species.     

Valence of elements in HgBa2Can-1CunO2n+2+d (n=1, 2, 3, 4)

Valence of elements in HgBa2Can-1CunO2n+2+d (n=1, 2, 3, 4) (both argon and oxygen annealed samples) were calculated. The result indicated for both argon and oxygen annealed samples, Hg had the lowest valence for the highest Tc sample. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produce more carriers than argon annealed samples.     

One-pot synthesis of [1+1] and 62-membered [2+2] Schiff base macrocycles

New [1+1] and 62-membered [2+2] Schiff base macrocycles containing a 2,6-diamidopyridine subunit have been synthesized by condensation reaction of the precursors pyridine-2,6-dicarboxamide and 1,10-bis(20-formylphenyloxy)decane in the presence of phosphoric acid via a one-pot process. The cyclocondensed products were effectively isolated by gel column chromatography and characterized by ~1H NMR, FTIR, mass spectrometry and X-ray analysis. The two macrocycles have a twisted structure, and not an open ‘circular' conformation in the solid state.     

Vapour–liquid equilibrium for the ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane

Isothermal vapour–liquid equilibrium was measured for ethyl ethanoate + 1-butene, +cis-2-butene, +trans-2-butene, +2-methylpropene, +n-butane and +2-methylpropane at 318.4 K with an automated static total pressure measurement apparatus. The experimental data was correlated with the Wilson activity coefficient model. A good agreement between the experiments and the model was achieved. All six binary systems exhibited positive deviation from Raoult's law.