Synthesis of (bis)Silicon Complexes of [38], [37], and [36]Octaphyrins: Aromaticity Switch and Stable Radical Cation

Silicon complexation of a [38]octaphyrin ( 1 ) was accomplished by reaction with an excess amount of MeSiCl₃ in the presence of N,N‐diisopropylethylamine, thus giving an aromatic [38]octaphyrin bis(silicon) complex 2 . This complex was interconvertible with an antiaromatic [36]octaphyrin congener ( 3 ) by oxidation with MnO₂ and reduction with NaBH₄. Curiously, mild oxidation of 2 with ferrocenium hexafluorophosphate afforded a [37]octaphyrin bis(silicon) complex 4 as an stable radical cation that can be stored under ambient conditions in the solid state. Owing to the two NNNCC‐five‐coordinated Si atoms bearing trigonal bipyramidal geometry, these octaphyrin bis(silicon) complexes take on similar and rigid figure‐of‐eight structures with different consecutive numbers of conjugated π‐electrons (38, 37, and 36), and are all stable.     

Meso-substituted [34]octaphyrin(1.1.1.0.1.1.1.0) and corrole formation in reactions of a dipyrromethanedicarbinol with 2,2'-bipyrrole

The reaction of a dipyrromethanedicarbinol with 2,2'-bipyrrole leading to meso-substituted [34]octaphyrin(1.1.1.0.1.1.1.0) and/or corrole was investigated to determine the effect of key reaction parameters on the distribution of the two macrocycles. Solvent, acid catalyst, acid quantity, oxidant, oxidant quantity, and reaction time were surveyed for a model reaction affording 5,10,19,24,29,38-hexaphenyl[34]octaphyrin(1.1.1.0.1.1.1.0) (HPO) and/or meso-triphenylcorrole (TPC). HPO was found to be a fairly ubiquitous product, produced in yields as high as 23% (UV-vis), while TPC was observed infrequently, in yields up to 10% (UV-vis). A preparative-scale reaction provided HPO in an isolated yield of 25%. The methodology was extended to the synthesis of an octaphyrin bearing two different substituents in defined locations and to an octaphyrin possessing electron-withdrawing pentafluorophenyl substituents. Preferential formation of octaphyrin instead of corrole suggests that the anti conformation of 2,2'-bipyrrole is the relevant form under the reaction conditions surveyed. The spectral properties of the novel meso-substituted [34]octaphyrin(1.1.1.0.1.1.1.0) species are similar to those of the known beta-substituted analogue, including spectra consistent with the absence of macrocycle aromaticity despite a main conjugation path of 34 pi-electrons. Key to the overall study was the development of a refined synthesis of 2,2'-bipyrrole.     

Rhodium N-heterocyclic carbene-catalyzed [4 + 2] and [5 + 2] cycloaddition reactions

[reactions: see text] A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular [4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal NHC complex in a Diels-Alder-type reaction. For the intramolecular [4 + 2] cycloaddition reactions, all the dienynes studied were converted to their corresponding cycloadducts in 91-99% yields within 10 min. Moreover, up to 1900 turnovers have been obtained for the intramolecular [4 + 2] cycloaddition at 15-20 degrees C. For the intermolecular [4 + 2] cycloadditions, high yields (71-99%) of the corresponding cycloaddition products were obtained. The reaction time and yield were highly dependent upon the diene and the dienophile. For the intramolecular [5 + 2] cycloaddition reactions, all the alkyne vinylcyclopropanes studied were converted to their corresponding cycloadducts in 91-98% yields within 10 min. However, the catalytic system was not effective for an intermolecular [5 + 2] cycloaddition reaction.     

Mechanically facilitated retro [4+2] cycloadditions

Poly(methyl acrylate)s (PMAs) of varying molecular weights were grown from a [4+2] cycloaddition adduct of maleimide with furan containing two polymerization initiators. Subjecting the corresponding PMA (>30 kDa) chains to ultrasound at 0 °C resulted in a retro [4+2] cycloaddition reaction, as observed by gel permeation chromatography (GPC) and UV-vis spectroscopy, as well as labeling of the liberated maleimide and furan moieties with appropriate chromophores featuring complementary functional groups. Similar results were obtained by sonicating analogous polymers that were grown from a thermally robust [4+2] cycloaddition adduct of maleimide with anthracene. The generation of anthracenyl species from these latter adducts allowed for the rate of the corresponding mechanically activated retro [4+2] cycloaddition reaction to be measured. No reduction in the number average molecular weight (M(n)) or liberation of the maleimide, furan, or anthracene moieties was observed (i) for polymers containing the cycloaddition adducts with M(n) < 20 kDa, (ii) for high molecular weight PMAs (M(n) > 60 kDa) featuring terminal cycloaddition adducts, or (iii) when the cycloaddition adducts were not covalently linked to a high molecular weight PMA. Collectively, these results support the notion that the aforementioned retro [4+2] cycloaddition processes were derived from a vectorially opposed mechanical force applied to adducts embedded within the polymer chains.     

Asymmetric synthesis of bicyclo[4.3.1]decadienes and bicyclo[3.3.2]decadienes via [6 + 3] trimethylenemethane cycloaddition with tropones

The cyanosubstituted trimethylenemethane donor undergoes palladium-catalyzed [6 + 3] cycloaddition with a variety of tropones to yield bicyclo[4.3.1]decadienes in excellent regio-, diastereo-, and enantioselectivity. Products of the Pd-TMM [6 + 3] cycloaddition participate in a thermal [3,3] sigmatropic rearrangement to yield bicyclo[3.3.2]decadienes in good yield.     

NHC-catalyzed enantioselective [2 + 2] and [2 + 2 + 2] cycloadditions of ketenes with isothiocyanates

The enantioselective N-heterocyclic carbene-catalyzed formal [2 + 2] and [2 + 2 + 2] cycloaddition of ketenes and isothiocyanates were developed. Reaction with N-aryl isothiocyanates at room temperature favors the [2 + 2] cycloaddition, while reaction with N-benzoyl isothiocyanates at -40 °C favors the [2 + 2 + 2] cycloaddition.     

Figure‐eight Octaphyrin Bis‐Ge(IV) Complexes: Synthesis,Structures, Aromaticity,and Chiroptical Properties

Highly twisted structures of expanded porphyrin provide a prominent basis to unravel the relationship between aromaticity and chirality. Here we report the synthesis of bis‐Ge(IV) complexes of [38]octaphyrin that display rigid figure‐eight structures. Two bis‐Ge(IV) [38]octaphyrin isomers with respect to the stereochemistry of the axial hydroxy groups on the germanium ions were obtained and found to be aromatic. Upon oxidation with MnO₂, these [38]octaphyrin complexes were converted to a single syn‐type isomer of [36]octaphyrin with retained figure‐eight conformation. The enantiomers have been successfully separated by HPLC equipped with a chiral stationary phase. While aromatic [38]octaphyrin Ge(IV) complexes showed quite large molar circular dichroism of up to Δ?=1500 M^?1cm^?1 with a dissymmetry factor g_abs of 0.035, weakly antiaromatic [36]octaphyrin Ge(IV) complexes underscored moderate values; Δ?=540 M^?1cm^?1 with g_abs of 0.023. Thus, the figure‐eight octaphyrin scaffold has been proved to be an attractive platform for novel chiroptical materials with tunable aromaticity.     

Palladium-catalyzed [3 + 3] cycloaddition of trimethylenemethane with azomethine imines

A palladium-catalyzed [3 + 3] cycloaddition of trimethylenemethane (TMM) with azomethine imines has been developed to produce hexahydropyridazine derivatives under simple and mild conditions. The use of substituted TMM precursors highlights the difference of this system from previously reported [3 + 2] cycloaddition of TMMs under palladium catalysis. The present [3 + 3] cycloaddition reactions are also applicable to couplings with nitrones.     

[60]富勒烯[2＋3]环加成反应的研究进展

对[60]富勒烯[2＋3]环加成反应的研究进展进行了综述，并介绍了在环加成反应中使用的主要试剂及反应机理.     

Synthesis of [1,3]dithiole and spiro[1,3]dithiole thiopyran derivatives of the [1,2]dithiolo[1,4]thiazine ring system

We report the synthesis of some new polysulfur-nitrogen heterocycles by cycloaddition reactions to readily available tricyclic condensed 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole ketothione 1 with diacyl acetylenes gave the bis-aducts 2a-d. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine ketothione 3 with 1 equiv of acyl or diacyl acetylenes gave [1,3]dithiolylidenyl[1,2]dithiolo[1,4]thiazines 4a-f in fair to high yields. Catalysis by scandium triflate was used in the reactions that implied the less reactive dipolarophiles. Treatment of 3 with 2 equiv of DBA gave the bis-aduct 5a, and reaction of 4c with DMAD gave the mixed bis-adduct 5b. Cyclic voltammetry of selected examples showed irreversible processes that were influenced by the electrochemical activity of peripheral groups bonded to the heterocyclic system.     

Catalytic Divergent [3+3]‐ and [3+2]‐Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α‐diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo[1,2‐a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported [3+3]‐cycloaddition of a carbonyl ylide. Use of Rh₂(pfb)₄ or Rh₂(esp)₂ directs the reactants to regioselective [3+2]‐cycloaddition generating cyclopenta[2,3]pyrrolo[2,1‐b]oxazoles with good yields and excellent diastereoselectivities.     

Microwave-assisted intramolecular [2 + 2] Allenic cycloaddition reaction for the rapid assembly of bicyclo[4.2.0]octa-1,6-dienes and bicyclo[5.2.0]nona-1,7-dienes

Microwave irradiation of alkynyl allenes affords an intramolecular [2 + 2] cycloaddition reaction. This cycloaddition provides an efficient route to bicyclomethylenecyclobutenes. The reaction occurs with complete regioselectivity for the distal double bond of the allene for the selective formation of a variety of hetero- and carbocyclic substrates. Bicyclo[4.2.0]octadienes and bicyclo[5.2.0]nonadienes have been prepared in high yield. [reaction: see text]     

Aryne [3 + 2] cycloaddition with N-sulfonylpyridinium imides and in situ generated N-sulfonylisoquinolinium imides: a potential route to pyrido[1,2-b]indazoles and indazolo[3,2-a]isoquinolines

The aryne [3 + 2] cycloaddition process with pyridinium imides breaks the aromaticity of the pyridine ring. By equipping the imide nitrogen with a sulfonyl group, the intermediate readily eliminates a sulfinate anion to restore the aromaticity, leading to the formation of pyrido[1,2-b]indazoles. The scope and limitation of this reaction are discussed. As an extension of this chemistry, N-tosylisoquinolinium imides, generated in situ from N'-(2-alkynylbenzylidene)-tosylhydrazides via an AgOTf-catalyzed 6-endo-dig electrophilic cyclization, readily undergo aryne [3 + 2] cycloaddition to afford indazolo[3,2-a]-isoquinolines in the same pot, offering a highly efficient route to these potential anticancer agents.     

Synthesis of A2B6‐Type [36]Octaphyrins: Copper(II)‐Metalation‐Induced Fragmentation Reactions to Porphyrins and N‐Fusion Reactions of meso‐(3‐Thienyl) Substituents

5,10,15‐Tris(pentafluorophenyl)tetrapyrromethane was efficiently prepared through a route involving stepwise diaroylation of 5‐pentafluorophenyldipyrromethane. A₂B₆‐type [36]octaphyrins were prepared by the cross condensation of the tetrapyrromethane with aryl aldehydes in moderate yields. A₂B₆‐type [36]octaphyrins bearing 2,4,6‐trifluorophenyl, 2,6‐dichlorophenyl, and phenyl substituents underwent Cu^II‐metalation‐induced fragmentation to give two molecules of AB₃‐type Cu^II porphyrins. A₂B₆‐type [36]octaphyrin bearing 3‐thienyl substituents underwent thermal N‐thienyl fusion reactions to provide a modestly aromatic [38]octaphyrin, which, upon treatment with MnO₂, underwent further N‐thienyl fusion and subsequent oxidation to give a nonaromatic doubly N‐thienyl fused [36]octaphyrin.     

Synthesis of 1-azacycl[3.2.2]azine and 1-azabenzo[h]cycl[3.2.2]azine

1-Azacycl[3.2.2]azines were synthesized from 2-methylthioimidazo[1,2-a]pyridines, 2a and 2b , by using [2 + 8] cycloaddition reaction with dimethyl acetylenedicarboxylate as the key step. Synthesis of 1-azabenzo-[h]cycl[3.2.2]azine was also described.     

Photocatalytic Oxidative [3+2] Cycloaddition for Pyrrolo[2,1-a]isoquinoline Synthesis Using a Porphyrin-Based Covalent Organic Framework

By using a catalytic amount of a porphyrin-based covalent organic framework (Por-Ad-COF) as the efficient recyclable photocatalyst, the photocatalytic oxidative [3+2] cycloaddition reaction between tetrahydroisoquinolines and N-substituted maleimides was developed under aerobic conditions at room temperature. Various substituted pyrrolo[2,1-a]isoquinolines were obtained in moderate to good yields via the dipolar [3+2] cycloaddition and oxidative aromatization cascade process under visible light irradiation. This was the first example to employ the covalent organic framework as the heterogeneous photocatalyst to perform the photocatalytic dipolar [3+2] cycloaddition reaction for the synthesis of pyrrolo[2,1-a]isoquinolines.     

新型色满酮并环己烷螺环氧化吲哚类化合物的合成

以色酮 氧化吲哚合成子与硝基苯乙烯,在催化剂DBU作用下,在二氯甲烷中发生Michael/Michael加成环化反应,合成了9个未见文献报道的新型色满酮并环己烷螺环氧化吲哚类化合物3a~3i产率72%~87%, dr值4/1~2/1, 其结构经¹H NMR, ¹³C NMR和HR-MS（ESI-TOF）表征确定。     

[6+2]Cycloadditions catalyzed by titanium complexes

The Ziegler catalyst TiCl₄-Et₂AlCl and the arenetitanium(II) complex (η6-C₆H₆)Ti(II)(AlCl₄)₂ induce [6 + 2]cycloaddition reactions of cycloheptatriene with dienes and acetylenes. Addition to 1,3-butadiene affords 7 - endo - vinyl - bicyclo[4.2.1]nona - 2,4 - diene (main product) and bicyclo[4.4.1]- undeca - 2,4,8 - triene, a product of [6+4]cycloaddition. Isoprene reacts similarly, yielding mainly 7- endo - isopropenyl - bicyclo[4.2.1]nona - 2,4 - diene. 2,3 - Dimethyl - 1,3 - butadiene gives 8,9dimethylbicyclo [4.4.1]undeca - 2,4,8 - triene, a product of [6 + 4]cycloaddition, while [6 + 2]cross-adducts are minor products. The reaction of cycloheptatriene with norbornadiene gives mainly hexacyclo[6.5.1.0^2,7.0^3,12.^6,10.0^9,13]tetradec - 4 - ene via [6+2]cycloaddition followed by intramolecular Diels-Alder reaction. As a by-product, pentacyclo[7.5.0.0^2,7.0^3,5.0⁴⁸]tetradeca - 10,12 - diene is formed by a [2+2+2]mechanism. Addition of cycloheptatriene to diphenylacetylene and bis - (tri- methylsilyl)acetylene furnishes sustituted bicyclo[4.2.1]nona - 2,4,7 - trienes. Alkenes, E,E-2,4 - hexadiene and 1,3 - cyclooctadiene are unreactive. The [6+2]cycloaddition is made possible by coordination of cycloheptatriene to titanium, which changes the symmetry of the frontier orbitals in the triene. The reactivity of the trienophile is also enhanced by coordination to the catalyst.     

Catalytic enantioselective [2 + 4] and [2 + 2] cycloaddition reactions with propiolamides

We report here the catalytic and highly enantioselective [2 + 4] and [2 + 2] cycloaddition reactions of electron-rich dienes or silyl enol ethers with electron-deficient propiolamide derivatives induced by copper(II).3-(2-naphthyl)-L-alanine amide complex.     

Photochemical formation of novel pyrrolo[3,2-b]-6,7-benzobicyclo[3.2.1]octa- 2,6-diene

The first synthesis of 1,4,9,10-tetrahydro-4,9-methanobenzo[4,5]cyclohepta[1,2-b]pyrrole (11) was achieved by the photochemical intramolecular [2 + 2] cycloaddition of N-phenoxycarbonyl- (5a) and N-ethoxycarbonyl-2-[2-(2-vinylphenyl)]pyrrole (6a), respectively, followed by basic hydrolysis of the isolated N-substituted 1,4,9,10-tetrahydro-4,9-methanobenzo[4,5]cyclohepta[1,2-b]pyrroles (10a, 10b). Some competitively formed products were also isolated.