Formal Synthesis of (±)‐Trachelanthamidine via Base‐Induced Formal [3+2] Annulation and Intramolecular Cyclization

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 an intramolecular cyclization. This facile strategy was used to synthesize (±)‐trachelanthamidine.     

catena‐Poly[[dichloridomercury(II)]‐μ‐1‐(2‐pyridylmethyl)‐1H‐benzotriazole]: the effect of different metal centers on the self‐assembly of coordination complexes

To further investigate the relationship between the structures of benzotriazol‐1‐yl‐based pyridyl ligands and their complexes, a new linear one‐dimensional Hg^II coordination polymer, [HgCl₂(C₁₂H₁₀N₄)]_n, with the 1‐(2‐pyridylmethyl)‐1H‐benzotriazole (L) ligand was obtained through the reaction of L with HgCl₂. In this complex, each Hg^II center within the one‐dimensional chain is coordinated by two chloride anions as well as by one pyridine and one benzotriazole N‐atom donor of two distinct L ligands in a distorted tetrahedral geometry, forming a linear one‐dimensional chain running along the [010] direction. Weak C—H...π and π–π stacking interactions link the one‐dimensional motifs to generate an overall two‐dimensional network parallel to the (100) plane. Comparison of the structural differences with previous findings suggests that the presence of different metal centers may plays an important role in the construction of such supramolecular frameworks.     

A Main‐Group Element Radical Based One‐Dimensional Magnetic Chain

The first main‐group element radical based one‐dimensional magnetic chain ( 1K )_n was realized by one‐electron reduction of the pyridinyl functionalized borane 1 with elemental potassium in THF in the absence of 18‐crown‐6 (18‐c‐6). The electron spin density of ( 1K )_n mainly resides at the boron centers with a considerable contribution from central benzene and pyridine moieties. The spin centers exhibit an antiferromagnetic interaction as demonstrated by magnetic measurements and theoretical calculations. In contrast, the reduction in the presence of 18‐c‐6 afforded the separated radical anion salt 1K(Crown) , in which the potassium cation was trapped by THF and 18‐c‐6 molecules. Further one‐electron reduction of 1K(Crown) and ( 1K )_n led to the diamagnetic monomer and polymer, respectively.     

Rhodium‐ and Iridium‐Catalyzed Asymmetric Addition of Optically Pure P‐Chiral H‐Phosphinates to Aldehydes Leading to Optically Active α‐Hydroxyphosphinates

Optically active α‐hydroxyphosphinates with both C‐ and P‐stereogenic centers are obtained by rhodium‐ or iridium‐catalyzed substrate‐directed stereoselective addition of the optically pure H‐phosphinates to aldehydes. The reaction most probably proceeds by a transition‐metal‐catalyzed mechanism with hydridometal complexes as key intermediates in the catalytic cycle.     

Poly­[[di­aqua­cobalt(II)]‐μ‐4,4′‐bi­pyridine‐κ2N:N′‐μ‐p‐phenyl­enebis­(oxy­acetato)‐κ2O:O′]

The title compound, [Co^II(C₁₀H₈O₆)(C₁₀H₈N₂)(H₂O)₂]_n, was obtained by the hydro­thermal reaction of CoSO₄ with benzene‐1,4‐dioxy­di­acetate [systematic name: p‐phenyl­ene­bis­(oxy­acetate)] and 4,4′‐bi­pyridine (4,4′‐bpy). The Co atom lies at an inversion center and the benzene‐1,4‐dioxydiacetate and 4,4′‐bipyridine moieties lie about other inversion centers. The benzene‐1,4‐dioxydiacetate ligands bridge the octahedral Co^II coordination centers, forming a one‐dimensional zigzag chain. The chains are further bridged by 4,4′‐bpy ligands, forming a novel two‐dimensional supramolecular architecture. Hydro­gen‐bonding interactions between the coordinated water mol­ecules and the carboxyl­ate O atoms lead to the formation of a three‐dimensional network structure.     

catena‐Poly[[bis[5‐(4‐pyridyl‐κN)‐2‐(2‐pyridylmethylsulfanyl)‐1,3,4‐oxadiazole]cadmium(II)]‐di‐μ‐thiocyanato‐κ2N:S;κ2S:N]

The title compound, [Cd(NCS)₂(C₁₃H₁₀N₄OS)₂]_n, contains SCN⁻ anions acting as end‐to‐end bridging ligands which utilize both S and N atoms to link cadmium(II) centers into one‐dimensional double chains. The multidentate 5‐(4‐pyridyl)‐2‐(2‐pyridylmethylsulfanyl)‐1,3,4‐oxadiazole ligands behave as monodentate terminal ligands, binding metal centers only through the N atoms of the 4‐pyridyl groups. Two types of eight‐membered rings are formed by two SCN⁻ anions bridging Cd^II centers, viz. planar and chair conformation, which are alternately disposed along the same chain. Finally, chains define a two‐dimensional array through two different interchain π–π stacking interactions.     

Quantum chemical calculation of exchange interactions in supramolecularly arranged N,N′‐dioxy‐2,6‐diazaadamantane organic biradical

Quantum mechanical exchange effects in purely organic N,N′‐dioxy‐2,6‐diazaadamantane biradical derivatives with promesogenic substituents have been studied. To determine intermolecular exchange energies, packing conditions of the radical core units in layered liquid crystalline phases are simulated using the Gaussian 09 program. The broken symmetry approach gives J ≈ 7 cm^?1 for intramolecular ferromagnetic exchange interactions between nitroxyl radical centers in one molecule. Both ferromagnetic and antiferromagnetic intermolecular interactions are possible in this kind of systems according to the obtained calculation results. Depending on the mutual positioning and orientation of molecules, the intermolecular antiferromagnetic exchange constant can reach a value of ?50 cm^?1, and the intermolecular ferromagnetic constant a value of 10 cm^?1. The simultaneous presence of intramolecular and intermolecular exchange between spin‐carrying centers in this kind of supramolecularly ordered multispin systems is favorable for the formation of magnetically interacting chains and two‐dimensional networks. © 2016 Wiley Periodicals, Inc.     

Desymmetrization of 1,4‐Pentadien‐3‐ol by the Asymmetric 1,3‐Dipolar Cycloaddition of Azomethine Imines

Desymmetrization of the divinyl carbinol 1,4‐pentadien‐3‐ol was accomplished by the asymmetric 1,3‐dipolar cycloaddition of azomethine imines based on a magnesium‐mediated, multinucleating chiral reaction system utilizing diisopropyl (R,R)‐tartrate as the chiral auxiliary. The corresponding optically active trans‐pyrazolidines, each with three contiguous stereogenic centers, were obtained with excellent regio‐, diastereo‐, and enantioselectivity, with results as high as 99 % ee. This reaction was shown to be applicable to both aryl‐ and alkyl‐substituted azomethine imines. The use of a catalytic amount of diisopropyl (R,R)‐tartrate was also effective when accompanied by the addition of MgBr₂.     

New Tetracyclic Colchicinoids from the Reaction of N‐Deacetylthiocolchicine and N‐Deacetylcolchicine with Nitrous Acid and tert‐Butyl Nitrite

Reaction of N‐deacetylthiocolchicine ( 3 ) and N‐deacetylcolchicine ( 4 ) with nitrous acid (HONO) furnished the new tetracyclic colchicinoids 5 and 6 , as well as the Demyanov‐rearrangement products 7 and 8 . Starting from 3 , the pyrazole‐containing tetracycle 9 was obtained. The novel compounds were characterized spectroscopically, and an X‐ray crystal‐structure analysis of 5 allowed us to establish the absolute configurations at the stereogenic centers.     

Oxygenase‐Catalyzed Desymmetrization of N,N‐Dialkyl‐piperidine‐4‐carboxylic Acids

γ‐Butyrobetaine hydroxylase (BBOX) is a 2‐oxoglutarate dependent oxygenase that catalyzes the final hydroxylation step in the biosynthesis of carnitine. BBOX was shown to catalyze the oxidative desymmetrization of achiral N,N‐dialkyl piperidine‐4‐carboxylates to give products with two or three stereogenic centers.     

Conjugate Addition of Lithiated (S)‐4‐Isopropyl‐3‐ [(methylthio)methyl]‐5,5‐diphenyloxazolidin‐2‐one to Cinnamoyl Derivatives: Preparation of Enantiomerically Pure 1,4‐Diols

The Li derivative of (S)‐4‐isopropyl‐3‐[(methylthio)methyl]‐5,5‐diphenyloxazolidin‐2‐one (Li‐ 2 ; synthetically equivalent to a chiral formyl anion) adds to enones and enoates in a 1,4‐fashion. Best results are obtained with 1,3‐diarylpropenones (chalcones; Scheme 2), trityl enones, and 2,6‐di(tert‐butyl)‐4‐methoxyphenyl cinnamates (Scheme 3), with yields up to 80% and diastereoselectivities up to and above 99 : 1 of the products ( 5a – f and 8a , b , e ) containing three stereogenic centers! X‐Ray crystal‐structure analysis reveals that the C,C‐bond formation occurs preferentially with relative topicity ul (Re/Si; Fig. 2). The MeS group of the 1,4‐adducts can be replaced by RO groups in Hg²⁺‐assisted substitutions, with subsequent removal and facile recovery of the chiral auxiliary (Schemes 4–6). 4‐Hydroxycarbonyl derivatives (‘homoaldols') and mono‐, di‐, and trisubstituted 1,4‐diols are, thus, accessible in enantiomerically pure forms (cf. 15, 16 , and 18 – 20 ).     

catena‐Poly[[aquacopper(II)]‐μ‐hydroxido‐μ‐naphthalene‐1‐carboxylato‐κ2O:O′]: effect of a bulky aromatic skeleton in self‐assembly

In the title coordination polymer, [Cu(C₁₁H₇O₂)(OH)(H₂O)]_n, the Cu^II center is five‐coordinated by two O atoms from two different naphthalene‐1‐carboxylate (L) ligands, one O atom from one coordinated water molecule and two O atoms from two hydroxide anions. L ligands and hydroxide anions jointly bridge adjacent Cu^II centers to generate a one‐dimensional chain along the b‐axis direction. The results reveal that the steric bulk of the naphthalene ring system in L may play an important role in the formation of the title complex.     

Intermolecular π‐stacking and F...F interactions of fluorine‐substituted meso‐alkynylporphyrin

Two C2‐symmetric meso‐alkynylporphyrins, namely 5,15‐bis[(4‐butyl‐2,3,5,6‐tetrafluorophenyl)ethynyl]‐10,20‐dipropylporphyrin, C₅₀H₄₂F₈N₄, (I), and 5,15‐bis[(4‐butylphenyl)ethynyl]‐10,20‐dipropylporphyrin, C₅₀H₅₀N₄, (II), show remarkable π–π stacking that forms columns of porphyrin centers. The tetrafluorophenylene moieties in (I) show intermolecular interactions with each other through the F atoms, forming one‐dimensional ribbons. No significant π–π interactions are observed in the plane of the phenylene and tetrafluorophenylene moieties in either (I) or (II). The molecules of both compounds lie about inversion centers.     

Brønsted Acid Catalyzed [3+2]‐Cycloaddition of 2‐Vinylindoles with In Situ Generated 2‐Methide‐2H‐indoles: Highly Enantioselective Synthesis of Pyrrolo[1,2‐a]indoles

Pyrrolo[1,2‐a]indoles are privileged structural elements of many natural products and pharmaceuticals. An efficient one‐step process for their highly diastereo‐ and enantioselective synthesis, comprising a direct [3+2]‐cycloaddition, has been developed. A chiral BINOL‐derived phosphoric acid catalyzes the reaction of in situ‐generated 2‐methide‐2H‐indoles with 2‐vinylindoles, furnishing the target products incorporating three contiguous stereogenic centers as single diastereoisomers and with excellent yields and enantioselectivities.     

Stereoselective Synthesis of the Non‐Lactonic Portion of (Z)‐Cryptofolione and Approaches towards Its Conversion to (Z)‐Cryptofolione

The stereoselective synthesis of the non‐lactonic part of the natural G₂ checkpoint inhibitor, (Z)‐cryptofolione, has been accomplished. Butane‐1,4‐diol was used as the starting material, and the stereogenic centers were generated through L ‐proline‐catalyzed α‐aminoxylation and Maruoka asymmetric allylation. We attempted to convert this non‐lactonic moiety to (Z)‐cryptofolione via olefin cross‐metathesis reaction, but by this approach another naturally occurring lactonic compound, goniothalamin, was obtained.     

Thermal cyclization of 3‐azido‐2‐phenyl‐indan‐l‐one to 5h‐indeno[1,2‐b]indol‐10‐one

3‐Azido‐2‐phenylindan‐1‐one ( 4 ), which was obtained from 3‐chloro‐2‐phenylindan‐1‐one ( 3 ), cyclizes on thermolysis to 5H‐indeno[1,2‐b]indol‐10‐one ( 5 ). Reaction of 3‐azido‐2‐phenylindan‐1‐one ( 4 ) with triphenylphosphane gives 2‐phenyl‐3‐(triphenylphosphoranylideneamino)‐indan‐1‐one ( 6 ), which can be hydrolyzed to 3‐amino‐2‐phenylindan‐1‐one ( 7 ). Attempts to perform a similar cyclization sequence with 3‐chloro‐2‐pyridylindan‐1‐ones failed.     

First Total Synthesis of 9‐Hydroxy‐8H‐pyrano[3,2‐f]indol‐2‐one

A simple and efficient approach to synthesize a novel pyrrolocoumarin 9‐hydroxy‐8H‐pyrano[3,2‐f]indol‐2‐one ( 7 ) has been described. Starting from vanillin, the key intermediate 7‐methoxy‐1H‐indol‐6‐yl propiolate ( 6 ) was synthesized in six steps. Then, the target compound was obtained by forming pyrone‐ring and demethylation simultaneously in one step. A plausible mechanism invoking PtCl₄ catalyzed one‐step reaction of cyclization and demethylation was also presented.     

Helix‐sense‐selective copolymerization of triphenylmethyl methacrylate with chiral 2‐isopropenyl‐4‐phenyl‐2‐oxazoline

The asymmetric induction leading to a one‐handed helix was investigated in the anionic and radical copolymerization of triphenylmethyl methacrylate (TrMA) and (S)‐2‐isopropenyl‐4‐phenyl‐2‐oxazoline ((S)‐IPO), and highly isotactic copolymers with a reasonable optical activity were obtained. In the anionic copolymerization, the optical activity of the obtained copolymers depended on the polarity of solvents, and a highly optically active copolymer was produced in the copolymerization in toluene. The chiral oxazoline monomer functioned not only as a comonomer but also as a chiral ligand to endow the polymer with large negative optical rotation in the copolymerization with TrMA. The copolymers with small positive optical rotation were obtained in THF, indicating that IPO unit may work only as the chiral monomer that dictates the helical sense via copolymerization with TrMA. The isotacticity of the obtained copolymers depended on the contents of TrMA units in the copolymers, but was almost independent of the solvent for copolymerization. In the radical copolymerization, the obtained copolymers exhibited small optical activities. It seemed that the chiral monomer cannot induce one‐handed helical structure of TrMA sequences even if the sequences probably have a high isotacticity. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 441–447     

Coordination‐Induced Spin‐State Switching of an Aminyl‐Radical‐Bridged Nickel(II) Porphyrin Dimer between Doublet and Sextet States

A bis(Ni^II‐porphyrinyl)aminyl radical with meso‐C₆F₅ groups was prepared as a spin‐delocalized stable aminyl radical with a doublet spin state. Upon addition of pyridine, both Ni^II centers became hexacoordinated by accepting two axial pyridines, which triggered a spin‐state change of the Ni^II centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high‐spin Ni^II centers interact with the aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination‐induced spin‐state switching can be conducted in a reversible manner, in that washing of the high‐spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.     

A Photoredox‐Induced Stereoselective Dearomative Radical (4+2)‐Cyclization/1,4‐Addition Cascade for the Synthesis of Highly Functionalized Hexahydro‐1H‐carbazoles

A stereoselective synthesis of functionalized hexahydrocarbazoles was developed based on an unprecedented photoredox‐induced dearomative radical (4+2)‐cyclization/1,4‐addition cascade between 3‐(2‐iodoethyl)indoles and acceptor‐substituted alkenes. The title reaction simultaneously generates three C−C bonds and one C−H bond, along with three contiguous stereogenic centers. The hexahydro‐1H ‐carbazole products are highly valuable intermediates for the synthesis of novel antibiotics, as well as unnatural ring homologues of polycyclic indoline alkaloids.