Neo‐Fused Hexaphyrin: A Molecular Puzzle Containing an N‐Linked Pentaphyrin

The first neo‐confused hexaphyrin(1.1.1.1.1.0) was synthesized by oxidative ring closure of a hexapyrrane bearing two terminal “confused” pyrroles. The new compound displays a folded conformation with a short interpyrrolic C???N distance of 3.102 Å, and thus it readily underwent ring fusion to afford a neo‐fused hexaphyrin with an unprecedented 5,5,5,7‐tetracyclic ring structure. Furthermore, coordination of Cu^II triggered a ring opening/contracting reaction to afford a Cu^II complex of an N‐linked pentaphyrin derivative. The roles of reactive N? C bonds in the porphyrinoid macrocycles were demonstrated.     

Hückel and Möbius Expanded para‐Benziporphyrins: Synthesis and Aromaticity Switching

The four expanded p‐benziporphyrins A,C‐di‐p‐benzi[24]pentaphyrin(1.1.1.1.1), N‐fused A‐p‐benzi[24]pentaphyrin, A,D ‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1), and A,C‐di‐p‐benzi[28]hexaphyrin(1.1.1.1.1.1) were obtained in three‐component Lindsey‐type macrocyclizations. These compounds were explored as macrocyclic ligands and as potential aromaticity switches. A BODIPY‐like difluoroboron complex was obtained from the A,C‐di‐p‐benzi[24]pentaphyrin, whereas A,C‐di‐p‐benzi[28]hexaphyrin yielded a Möbius‐aromatic Pd^II complex containing fused pyrrole and phenylene subunits. Conformational behavior, tautomerism, and acid‐base chemistry of the new macrocycles were characterized by means of NMR spectroscopy and DFT calculations. Free base N‐fused A‐p‐benzi[24]pentaphyrin showed temperature‐dependent Hückel–Möbius aromaticity switching, whereas the A,C‐di‐p‐benzi[28]hexaphyrin formed a Möbius‐aromatic dication.     

N‐Confused Phlorin‐Prodigiosin Chimera: meso‐Aryl Oxidation and π‐Extension Triggered by Peripheral Coordination

An N‐confused phlorin isomer bearing a dipyrrin moiety at the α‐position of the confused pyrrole ring ( 1 ) was synthesized. Pd^II and B^III coordination at the peripheral prodigiosin‐like moiety of 1 afforded the corresponding complexes 2 and 3 . Reflux of 2 in triethylamine (TEA) converted the meso‐phenyl into the Pd^II‐coordinating phenoxy group to afford 4 . Under the same reaction conditions, TEA was linked to the α‐position of the dipyrrin unit in 3 as an N,N‐diethylaminovinyl group to afford 5 . Furthermore, peripheral coordination of B^III in 3 and 5 improved the planarity of the phlorin macrocycle and thus facilitated the coordination of Ag^III at the inner cavity to afford 3‐Ag and 5‐Ag , respectively. These results provide an effective approach for developing unique porphyrinoids through peripheral coordination.     

Rational Synthesis of 5,5,5‐Tricyclic Fused Thia‐heptaphyrin (1.1.1.1.1.1.0) From a Helical Oligopyrrin Hybrid

Oxidation of a thiophene‐hexapyrrane hybrid S‐P₆ afforded a stable conjugated open‐chain thiaheptapyrrolic helix 1 with the terminal thiophene and confused pyrrole units lying at a long distance that is adverse for further cyclization. Chelation of 1 with copper(II) ion afforded 1‐Cu , which exhibits more distant terminal units. Interestingly, further oxidation of 1 triggered an intramolecular C?N fusion reaction to afford a unique 5,5,5‐tricyclic fused linear thiaheptapyrrin 2 , with the two terminals positioned in proximity, which favors the oxidative ring‐closure reaction to give a unique 5,5,5‐tricyclic fused thiaheptaphyrin (1.1.1.1.1.1.0) 3 under air. The inner‐fusion strategy for positioning the reactive sites in proximity to promote oxidative cyclization offers a new approach for constructing large porphyrinoids through conjugated oligopyrrins without the assistance of metal ions.     

Siamese‐Twin Porphyrin Origami: Oxidative Fusing and Folding

Oxidation of a nonaromatic Siamese‐twin porphyrin, a pyrazole‐containing expanded porphyrin with two porphyrinlike binding pockets, with a stoichiometric amount of the two‐electron, two‐proton oxidizing agent 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzochinone led to the formation of a single N^pz‐C^o‐Ph linkage between the pyrazole unit with a neighboring meso‐phenyl group, forming a pyrazolo‐ [1,5‐a]indole moiety. Repeated treatment with a second equivalent of the oxidant yielded a doubly N‐fused species, involving the second pyrazole moiety. The conversion products were characterized by variable‐temperature and multinuclear 1D and 2D NMR spectroscopy. The fusions strongly alter the conformation of the macrocycles, as shown by X‐ray diffraction analyses of all three compounds, eventually leading to a folded structure. UV/Vis and NMR‐spectroscopic investigations indicated the presence of highly delocalized but nonmacrocycle‐aromatic π systems. This behavior of the Siamese‐twin porphyrin in response to oxidation is in contrast to the behavior of related all‐pyrrole‐based expanded macrocycles that switch, by redox processes and protonation, between Hückel and Möbius aromatic states.     

Doubly N‐Fused [24]Pentaphyrin Silicon Complex and Its Fluorosilicate: Enhanced Möbius Aromaticity in the Fluorosilicate

Treatment of nonaromatic N‐fused [24]pentaphyrin with trichloromethylsilane in the presence of a base afforded doubly N‐fused [24]pentaphyrin and its silicon complex. Addition of fluoride ion to the silicon complex led to the formation of its fluorosilicate as an unprecedented monoanionic six‐coordinated Si^IV complex of porphyrinoid. Treatment of the fluorosilicate with acid led to the recovery of the silicon complex. The doubly N‐fused pentaphyrin, the silicon complex, and the fluorosilicate were all characterized as distinct Möbius aromatic molecules by spectroscopic measurements and X‐ray crystallographic analyses. Importantly, the second N‐fusion reaction, Si‐incorporation and fluoride addition to the Si‐atom enhanced the aromaticity of doubly N‐fused [24]pentaphyrins in this order. Tamao–Fleming oxidation of the silicon complex gave β‐keto doubly N‐fused pentaphyrin and triply fused [24]pentaphyrin, which were nonaromatic and Hückel anti‐aromatic, respectively.     

Boron Difluoride Complexes of Expanded N‐Confused Calix[n]phyrins That Demonstrate Unique Luminescent and Lasing Properties

Complexation of novel multiply N‐confused expanded calix[n]phyrins with boron difluoride afforded a new class of cyclic BODIPY (boron‐dipyrromethene) arrays. The structures of circularly arranged BODIPY subunits linked in an N‐confused fashion give rise to such photophysical properties unique to the macrocycles as redshifted emission wavelengths along with apparent large Stokes shifts, long emission lifetimes, and solid‐state lasing. The DFT calculations support the size‐dependent excited‐state dynamics of the macrocycles.     

N-Confused Phlorin-Prodigiosin Chimera: meso-Aryl Oxidation and π-Extension Triggered by Peripheral Coordination

An N-confused phlorin isomer bearing a dipyrrin moiety at the α-position of the confused pyrrole ring ( 1 ) was synthesized. Pd^II and B^III coordination at the peripheral prodigiosin-like moiety of 1 afforded the corresponding complexes 2 and 3 . Reflux of 2 in triethylamine (TEA) converted the meso-phenyl into the Pd^II-coordinating phenoxy group to afford 4 . Under the same reaction conditions, TEA was linked to the α-position of the dipyrrin unit in 3 as an N,N-diethylaminovinyl group to afford 5 . Furthermore, peripheral coordination of B^III in 3 and 5 improved the planarity of the phlorin macrocycle and thus facilitated the coordination of Ag^III at the inner cavity to afford 3-Ag and 5-Ag , respectively. These results provide an effective approach for developing unique porphyrinoids through peripheral coordination.     

Incorporation of a Phenanthrene Subunit into a Sapphyrin Framework: Synthesis of Expanded Aceneporphyrinoids

32‐Hetero‐5,6‐dimethoxyphenanthrisapphyrins—macrocycles that link structural features of polycylic aromatic hydrocarbons and expanded porphyrins—were obtained in a straightforward [3+1] condensation reaction of dimethoxyphenanthritripyrrane and 2,5‐bis(arylhydroxymethyl)heterocyclopentadienes. The highly folded conformation of formally 4 n π‐electron macrocycles causes them to manifest only limited macrocyclic π conjugation as explored by means of NMR spectroscopic and X‐ray structural analyses, and supported by DFT calculations. Although protonation does not change their π‐conjugation characteristics, the cleavage of ether groups at the phenanthrenylene moiety yields nonaromatic 32‐hetero‐5,6‐dioxophenanthrisapphyrins.     

Iridium‐Catalyzed Annulation Reactions of Thiophenes with Carboxylic Acids: Direct Evidence for a Heck‐type Pathway

The functionalization of thiophenes is a fundamental and important reaction. Herein, we disclose iridium‐catalyzed one‐pot annulation reactions of (benzo)thiophenes with (hetero)aromatic or α,β‐unsaturated carboxylic acids, which afford thiophene‐fused coumarin‐type frameworks. Dearomatization reactions of 2‐substituted thiophenes with α,β‐unsaturated carboxylic acids deliver various thiophene‐containing spirocyclic products. The occurrence of two interconnected reactions provides direct evidence for a Heck‐type pathway. The mechanistic scenario described herein is distinctly different from the S_EAr and concerted metalation–protodemetalation (CMD) pathways encountered in the well‐described oxidative C?H/C?H cross‐coupling reactions of thiophenes with other heteroarenes.     

Expanded Carbaporphyrinoids

This Review outlines the progress in the field of synthetic expanded carbaporphyrinoids. The evolution of this topic is demonstrated with expanded porphyrin‐inspired systems with a variety of incorporated entities that introduce one or more carbon atoms into the cavity. The discussion starts with platyrins—the macrocycles that were identified as parent molecules of not only the expanded carbaporphyrinoids, but the carbaporphyrinoid class in general. After historic considerations, the plethora of expanded porphyrin‐like macrocycles containing N‐confused or neo‐confused pyrrole motifs and different carbocyclic subunits are presented. Special emphasis is given to applications of expanded carbaporphyrinoids in different areas, including organometallic chemistry, switching systems, or aromaticity, concluding with the demonstration of a covalent cage based on an expanded carbaporphyrinoid.     

Macrocyclic Transformations from Norrole to Isonorrole and an N‐Confused Corrole with a Fused Hexacyclic Ring System Triggered by a Pyrrole Substituent

Three kinds of fused porphyrinoids, L2 – L4 , possessing different types of corrole‐based frameworks were synthesized from a pyrrole‐substituted corrole isomer (norrole L1 ). Oxidation of L1 afforded a unique N‐C_meso‐fused pyrrolyl isonorrole L2 , involving the fusion of an auxiliary pyrrolic NH moiety with a meso‐sp³‐hybridized carbon atom. Subsequently, L2 underwent macrocycle transformations to give singly and doubly N‐C_Ar‐fused N‐confused corroles, L3 and L4 , respectively. L3 and L4 contain fused [5.7.6.5]‐tetra‐ and [5.6.7.7.6.5]‐hexacyclic structures, respectively, prepared through lateral annulation. These skeletal transformation reactions from norrole to its isomer isonorrole and finally to N‐confused corrole indicate that multiply fused porphyrinoids could be readily synthesized from pyrrole‐appended confused porphyrinoids.     

Synthesis and properties of calixarene analogs incorporating a thiophene unit in the macrocyclic ring

Calixarene analogs containing a thiophene unit in the macrocyclic ring were prepared by a stepwise method. The macrocycles adopt a cone‐like form as the preferred conformation in solution. The induced chemical shift change, nOe experiment, and ¹H relaxation time (T₁) measurement supported the fact that the macrocycle forms a complex with the N‐methylpyridinium salt. In contrast, O‐tetramethylated macrocycles and linear phenol‐formaldehyde tetramer, could not efficiently include the N‐methylpyridinium salt.     

Au/Pd(111)双金属表面催化噻吩加氢脱硫的反应机理

采用密度泛函理论(DFT)计算了Pd(111)表面含有N(N=1-4)个Au原子数目时的表面形成能,选取最优构型进一步研究了噻吩在Au/Pd(111)双金属表面的吸附模式及加氢脱硫反应过程.结果表明:当Pd(111)表面含有1个Au原子时,其形成能最低.在Au/Pd(111)双金属表面噻吩初始吸附于Pd-Hcp-30°位时,其构型最稳定.在各加氢脱硫过程中,反应总体均放出热量.对于直接脱硫机理,其所需活化能较低,但脱硫产物较难控制;对于间接脱硫机理,反应最有可能按照顺式加氢方式进行,C―S键断裂开环时所需活化能最高,是反应的限速步骤.此外,与单一Au(111)面及Pd(111)面相比,Au/Pd(111)双金属表面限速步骤的反应能垒最低,表明AuPd双金属催化剂比Au、Pd单金属催化剂更有利于噻吩加氢脱硫反应的进行.     

Au/Pd(111)双金属表面催化噻吩加氢脱硫的反应机理

采用密度泛函理论（DFT）计算了Pd（111）表面含有N（N=1-4）个Au原子数目时的表面形成能,选取最优构型进一步研究了噻吩在Au/Pd（111）双金属表面的吸附模式及加氢脱硫反应过程. 结果表明：当Pd（111）表面含有1个Au原子时,其形成能最低. 在Au/Pd（111）双金属表面噻吩初始吸附于Pd-Hcp-30°位时,其构型最稳定. 在各加氢脱硫过程中,反应总体均放出热量. 对于直接脱硫机理,其所需活化能较低,但脱硫产物较难控制;对于间接脱硫机理,反应最有可能按照顺式加氢方式进行,C―S键断裂开环时所需活化能最高,是反应的限速步骤. 此外,与单一Au（111）面及Pd（111）面相比,Au/Pd（111）双金属表面限速步骤的反应能垒最低,表明AuPd双金属催化剂比Au、Pd单金属催化剂更有利于噻吩加氢脱硫反应的进行.     

Short Review on the Synthesis of Thiophene,Pyrazole, and Thiazole Derivatives

The review summarizes the synthesis of different thiophene, pyrazole, and thiazole derivatives by refluxing 9a in ethanol with a catalytic amount of TEA or leaving it in DMF containing potassium carbonate at room temperature overnight to afford the corresponding thiophene derivative 10a . In addition, cyclization of Schiff bases with thioglycollic acid in the presence of a catalytic amount of ZnCl₂ yielded novel thiophene derivatives. Condensation of 2‐substituted‐4‐methylythio semi‐carbazides 92 with carbonyl compounds under strong acidic conditions afforded 2‐thiazolines. Also, carboxylic acid reacted with 2‐thioethylamine in the presence of triphenylphosphine and triethylamine to afford 2‐thiazolines 98 .     

Stacking patterns of thieno[3,2‐b]thiophenes functionalized by sequential palladium‐catalyzed Suzuki and Heck cross‐coupling reactions

The crystal structures of three 5‐alkenyl‐2‐arylthieno[3,2‐b]thiophenes, namely 3,6‐dibromo‐5‐(4‐tert‐butylstyryl)‐2‐(naphthalen‐1‐yl)thieno[3,2‐b]thiophene, C₂₈H₂₂Br₂S₂, (I), 3,6‐dibromo‐5‐(4‐methylstyryl)‐2‐(naphthalen‐1‐yl)thieno[3,2‐b]thiophene, C₂₅H₁₆Br₂S₂, (II), and 3,6‐dibromo‐2‐(4‐tert‐butylphenyl)‐5‐(4‐methylstyryl)thieno[3,2‐b]thiophene, C₂₅H₂₂Br₂S₂, (III), have been determined in order to evaluate the geometry of the molecules. The π‐conjugated system containing the thieno[3,2‐b]thiophene skeleton, the ethylene bridge and the phenyl rings is almost planar. The aromatic ring directly attached to the thieno[3,2‐b]thiophene moiety is not coplanar with the thieno[3,2‐b]thiophene moiety itself due to steric hindrance of the bromo substituent. The crystal packings are characterized by π–π stacking [only for (II)] and C—Br...π interactions. The long axes of the molecules in (I) are oriented in two directions; for the two other structures the long axis is oriented in one direction only.     

Efficient Synthesis of Highly Substituted Furan,Thiophene, Pyrrole and 2‐Aminothiazole Derivatives

Ethyl cyanoacetate dimer (1) undergoes bromination with N‐bromosuccinimide (NBS) to afford 3‐amino‐4‐bromo‐2‐cyano‐pent‐2‐enedioic acid diethyl ester (2). This bromo derivative reacts with potassium carbonate, sodium hydrogen sulfide, aromatic amines, ammonium thiocyanate, thiourea, N‐phenylthiourea, and thiosemicarbazide to afford highly substituted furan, thiophene, pyrrole, and 2‐aminothiazole derivatives. Mechanistic explanations as well as structure elucidations are discussed.     

The induced current strengths and aromatic pathways of heteroporphyrins and their antiaromatic derivatives

The magnetically induced current strengths as well as nucleus independent chemical shifts of aromatic heteroporphyrins and antiaromatic 22,24‐dideazaheteroporphyrins have been studied using the density functional theory method. The induced current strengths and pathways are obtained by numerical integration of the induced current densities following the specific chemical bonds. The total induced current strengths of antiaromatic 22,24‐dideazaheteroporphyrins is about 6 nA/T weaker than the one for the heteroporphyrins in absolute value. The substitution of pyrrole NH groups by O and S atoms does not change the total induced current strengths. The induced currents around the molecular macroring split at the heterocycles (pyrrole, furan, and thiophene) into the inner and outer routes. The heteroatoms (N, O, and S) have high resistance and consequently lead to a weaker induced current strength than the one passing the outer route in aromatic heteroporphyrins. For antiaromatic 22,24‐dideazaheteroporphyrins, the heteroatoms enhance the current strength and change the main current pathway into the inner route. The induced current strength following the NH moiety is stronger than the one passing the oxygen moiety of furan ring and the sulfur moiety of the thiophene ring in both heteroporphyrins and 22,24‐dideazaheteroporphyrins. © 2015 Wiley Periodicals, Inc.     

Synthesis and Switching the Aromatic Character of Oxatriphyrins(2.1.1)

Triangularly shaped, contracted porphyrinoids belong to a group of molecules where the geometry significantly modifies the observed electronic properties. The need for a controllable, effective, and widely applicable approach to triphyrins drives extensive research towards macrocyclic materials that act as potential controlling motifs by switching their aromaticity. Two isomeric thiophene‐fused triphyrins(2.1.1) were synthesized by applying an innovative approach. Spectroscopic techniques (NMR, UV/Vis) show that both macrocycles are aromatic and quantitatively convert into anti‐aromatic structures after reduction with a zinc amalgam. The reduced forms were stabilized through boron(III) coordination, thereby allowing the observation of anti‐aromatic 16 π delocalization within a contracted porphyrin.