The synthesis of new tetrabenzo- and tetranaphthoporphyrins via the addition reactions of 4,7-dihydroisoindole

The double bond in 4,7-dihydroisoindole derivatives was shown to be a useful reaction site to afford new porphyrinogenic pyrrolic precursors bearing substituted annelated rings via various addition reactions. These precursors are further used to afford new extended porphyrins substituted in the annelated rings. The Sharpless osmium-catalyzed dihydroxylation of dihydroisoindole system was shown to be useful in the synthesis of non-ionogenic water-soluble porphyrin, as well as tetrabenzoporphyrin bearing acetoxy-substituents in benzo-rings. The reverse electron-demand Diels-Alder reaction with tetrachlorothiophene-1,1-dioxide afforded new polychlorosubstituted tetranaphthoporphyrin.     

New chiral zinc complexes: synthesis, structure, and induction of axial chirality

We describe an efficient methodology for the preparation of new chiral zinc complexes by assembling dynamically racemic biphenol derivatives and chiral 1,2-diamines with suitable zinc(II) precursors. Mononuclear and dinuclear zinc(II) complexes were formed from differently substituted biphenols. The solid-state and solution structural characterization of the resulting compounds allowed us to demonstrate a preferential sense of induced axial chirality for mononuclear complexes, a phenomenon that was not observed for the dinuclear ones.     

Syntheses of dibenzo[b,e][1,4]dioxin derivatives via iron complexes, and further functionalizations via directed metallation

Double nucleophilic aromatic substitution reactions between (cyclopentadienyl)(η⁶-1,2-dichlorobenzene)iron(1 + ) salts and substituted 1,2benzenediols have been carried out under mild conditions to prepare [η⁶-dibenzo[b,e][1,4]dioxin]iron(1 + ) complexes functionalized in the 1- or 2-position with an alkyl, aldehyde, carboxylic acid, methoxycarbonyl, carboxamide, or hydroxy group. 3-Methyl- and 4-methyl-(η⁶-1,2-dichlorobenzene)iron complexes were treated with substituted 1,2-benzenediols to effect functionalization of both aromatic rings of the heterocycle. The dibenzodioxin ligands were liberated routinely by irradiation with ultraviolet light. Directed deprotonation of the free functionalized dibenzodioxins with an alkyllithium reagent followed by quenching with a variety of electrophiles yielded further derivatives, including two new isoindolone systems.     

Co-ordination behaviour of a novel bisthiourea tripodal ligand: structural, spectroscopic and electrochemical properties of a series of transition metal complexes

The synthesis of a thiourea substituted derivative of tris(pyridyl-2-methyl)amine (TPA) is reported. Two of the three pyridine rings are substituted in the 6-position with benzoylthiourea groups. These thiourea groups undergo intramolecular hydrogen bonding to form six-membered rings which leaves one N-H group available to form hydrogen bonds with other molecules. This reports details how the complexation of this new ligand with transition metal ions yields complexes with differing geometries. Seven co-ordinate Mn(II) and Cd(II), six co-ordinate Ni(II) and five co-ordinate Co(II), Cu(II) and Zn(II) complexes have been isolated.     

4H-1,2-benzoxazines with electron-withdrawing substituents on the benzene ring: synthesis and application as potent intermediates for oxygen-functionalized aromatic compounds

A new general method for synthesizing functionalized 4H-1,2-benzoxazine derivatives is described. Although 4H-1,2-benzoxazine is one of the fundamental structure of the oxazine group, no general synthetic method for the heterocycle has been established. We found that 3-methoxycarbonyl-4H-1,2-benzoxazine was obtained in good yield when methyl 2-nitro-3-phenylpropionate was treated with an excess amount of trifluoromethanesulfonic acid. This methodology was also applicable for the synthesis of 4H-1,2-benzoxazine rings functionalized with various electron-withdrawing substituents on the benzene ring. Furthermore, we also show that the resulting 4H-1,2-benzoxazines can be used as precursors of functionalized o-quinone methides and multisubstituted phenols. This type of heterocycle can be a potent intermediate to oxygen-fuctionalized aromatic compounds.     

Alkylation of Terminal Alkynes with Transient σ‐Alkylpalladium(II) Complexes: A Carboalkynylation Route to Alkyl‐Substituted Alkynes

A mild and general alkylation of terminal alkynes with transient σ‐alkylpalladium(II) complexes for assembling alkyl‐substituted alkynes is described. This method represents a new way to the use of transient σ‐alkylpalladium(II) complexes in organic synthesis through 1,2‐carboalkynylation of alkenes.     

Regiodivergent Addition of Phenols to Allylic Oxides: Control of 1,2‐ and 1,4‐Additions for Cyclitol Synthesis

Control of 1,2‐ and 1,4‐addition of substituted phenols to allylic oxides is achieved by intercepting palladium π‐allyl complexes. The interconversion of palladium complexes results in the total synthesis of MK 7607, cyathiformine B type, streptol, and a new cyclitol.     

Design of Schiff Base-Like Postmetallocene Catalytic Systems for Polymerization of Olefins: III. Synthesis of 1,2-Bis-(arylimino)acenaphthenes Having Cyclic Substituents

Reactions of substituted cycloalkylanilines with acenaphthenequinone in a mixture of methanol with methylene chloride afforded a number of the corresponding 1,2-is(cycloalkylarylimino)acenaphthenes. The products may be used as ligands for the synthesis of nickel complexes which are capable of catalyzing olefin polymerization at elevated temperature in the presence of methylaluminoxane.     

Functionalization of Heterocycles through 1,2-Metallate Rearrangement of Boronate Complexes

Over the last decade, 1,2-metallate rearrangement of boronate complex has been dominating the literature of organoboron chemistry for the construction of very important C−C and C−boron bonds. Owing to the coordinative unsaturated nature of the boron atom, a nucleophile can attack on boron center for the formation of a boronate complex, which triggers 1,2-migration under electrophilic activation at the α-carbon. Apart from using stochiometric electrophilic activating reagents, several catalytic methods using transition metals in the presence or absence of light have been reported. The 1,2-migration of boronate complexes allows synthesis of many different classes of racemic and chiral compounds including a wide range of substituted heterocycles. Synthesis of chiral and achiral substituted heterocycles by using 1,2-metallate rearrangement of boronate complexes has been extensively reported by several groups owing to its prevalence in medicinal chemistry. This minireview highlights the methods known to date for the synthesis of heteroaryls by using 1,2-migration of boronate complexes, organized in a chronological manner.     

Intramolecular domino electrophilic and thermal cyclization of peri-ethynylene naphthalene oligomers

The intramolecular electrophilic or thermal cyclization of arylene ethynylene precursors recently became a powerful method for the synthesis of new polycyclic aromatic hydrocarbons (PAHs). In this work, we investigated in detail the synthesis and intramolecular cyclization reaction of a series of peri-ethynylene naphthalene oligomers in which the ethynylene units are fixed in close proximity within the naphthalene framework. The high reactivity of these precursors led to simultaneous thermal cyclization reactions, even during their syntheses. Electrophilic cyclizations with iodine were also undertaken. Several new PAHs containing five-membered rings, for example, indeno[2,1-a]phenalene, acenaphtho[1,2-a]pyrene, and benzo- or naphtho-annulated fluoranthene derivatives, were synthesized and their structures were unambiguously determined by X-ray crystallographic analysis. Plausible mechanisms were proposed and it was demonstrated that oligomers most probably underwent intramolecular domino cyclization via either radical or cationic intermediates. The photophysical and electrochemical properties of these new PAHs were investigated and some of them displayed amphoteric redox behavior, due to the existence of five-membered rings.     

Synthesis of acyclic and cyclic phosphonates based on substituted 2-hydroxybenzylic alcohols

Russian Chemical Bulletin - A convenient synthesis of benzylic phosphonates and 2,3-dihydrobenzo[d][1,2]oxaphosphole 2-oxides substituted at the aromatic ring, as well as their precursors,...     

Visible-Light-Driven Strain-Increase Ring Contraction Allows the Synthesis of Cyclobutyl Boronic Esters

There are a limited number of ring-contraction methodologies which convert readily available five-membered rings into strained four-membered rings. Here we report a photo-induced radical-mediated ring contraction of five-membered-ring alkenyl boronate complexes into cyclobutanes. The process involves the addition of an electrophilic radical to the electron-rich alkenyl boronate complex, leading to an α-boryl radical. Upon one-electron oxidation, ring-contractive 1,2-metalate rearrangement occurs to give a cyclobutyl boronic ester. A range of radical precursors and vinyl boronates can be employed, and chiral cyclobutanes can be accessed with high levels of stereocontrol. The process was extended to the preparation of benzofused cyclobutenes and the versatility of the boronic ester was demonstrated by conversion to other functional groups.     

Helicenes Built from Silacyclopentadienes via Ring‐by‐Ring Knitting of the Helical Framework

Despite the apparent diversity of the protocols developed for the synthesis of helicenes, they essentially follow the same strategy: the closure of one, or several, internal rings in a key step. Herein, we report the synthesis of a new family of the heterohelicenes consisting of fused silacyclopentadiene rings formed via a facile and novel process. The treatment of oligo(alkynilydenesilylene) precursors of type H₂C=CH?(SiMe₂?C≡C)_n?R (n=3–7), bearing a vinyl group on the terminal silicon atom, with 9‐borabicyclononane leads first to 1,2‐hydroboration of the terminal double bond which then continues with a cascade of intramolecular 1,1‐carboboration reactions accompanied with the closure of a new silole ring after each step affording the target silahelicenes with, currently, up to seven condensed silole rings and with excellent yields. According XRD analysis, the seven fused silole rings of the heptacyclic compound 11 b form an almost complete turn of a helix. The presented one‐pot sequence of reactions is the first example of ring‐by‐ring knitting of a helical framework starting from easily available linear precursors.     

The synthesis of angularly fused polyaromatic compounds by using a light-assisted, base-mediated cyclization reaction

The synthesis of substituted polyaromatic compounds that contain at least four benzene rings fused together in an angular fashion is described. Suzuki coupling of 1-bromo-3,4-dihydronaphthalene-2-carbaldehyde with a number of aromatic boronic acids affords products such as 1-(1,4-dimethoxy-3-methyl-2-naphthyl)-3,4-dihydronaphthalene-2-carbaldehyde. Exposure of these dihydronaphthalenes to potassium tert-butoxide and DMF at 80 degrees C yields polyaromatic compounds such as 9,14-dimethoxynaphtho[1,2-a]anthracene.     

2]Borametallocenophanes of Zr and Hf: synthesis, structure, and polymerization activity

The first [2]borametallocenophanes of Zr and Hf are reported, which were obtained from 1,2-bis(dimethylamino)-1,2-dicyclopentadienyldiborane(4). The constitution of these complexes in solution and, for the Hf complex, in the crystalline state is discussed. The title complexes were studied as Ziegler-Natta-type catalyst precursors for the polymerization of ethylene. Both complexes produced PE of high molecular mass up to 1.6 x 106 g/mol, and very interestingly, the Hf complex proved to be as active as its Zr analogue.     

Generation of synthetic equivalents of benzdiynes from benzobisoxadisiloles

Linear and angular benzobisoxadisiloles 14 and 16 can serve as the precursors for stepwise generations of the syntetic equivalents of 1,4- and 1,3-benzdiynes. Benzynes generated were trapped as [4+2] cycloaddition products. Two identical or different rings can be fused to the benzdiyne equivalents. Highly substituted arenes were obtained by removing the oxygen bridges from the furan adducts. The synthesis of naphthoxadisilole 28, which can serve as the precursor of 2,3-naphthyne, is also described.     

Efficient palladium-catalyzed synthesis of unsymmetrical donor—acceptor biaryls and polyaryls

4,4′-Unsymmetrically substituted biphenyls can be synthesized by cross-coupling reactions of substituted aromatic organometallic reagents and aromatic halides catalyzed by palladium complexes. This two-step method from commercially available aromatic halides has been used for the synthesis of a series of donor/acceptor para-substituted biphenyls, D---C₆H₄---C₆H₄---A, where D is an electron donor group and A an electron acceptor group, which are of interest as liquid crystal precursors and as having potential in non-linear optics. Biaryls in which the donor-phenyl moiety is replaced by a 2-furyl or 2-thienyl can be synthesized similarly. The method can also be used for the convergent synthesis of previously unreported unsymmetrically substituted polyparaphenylenes (n = 3,4).     

Template synthesis of 9-membered triphospha-macrocycles with rigid o-phenylene backbone functions

[eta(5)-Cp(R)Fe(CH3CN)(1,2-diphosphinobenzene)]+ complexes are readily formed from [eta(5)-Cp(R)FeL3]+ salts and act as template precursors for the intramolecular hydrophosphination of co-ordinated trivinylphosphine with 1,2-diphosphinobenzenes. This sequence constitutes a versatile synthetic route to a new class of co-ordinated triphosphacyclononanes bearing a rigid o-phenylene backbone link. The efficiency of the synthesis depends markedly upon the nature of the Cp(R) ligand. The new secondary phosphine macrocycles prepared by this route are readily alkylated to tritertiary triphosphine macrocycles bearing alkyl and pendant functions.     

Synthesis of pyrido[1,2-a]indole malonates and amines through aryne annulation

Pyrido[1,2-a]indoles are known as medicinally and pharmaceutically important compounds, but there is a lack of efficient methods for their synthesis. We report a convenient and efficient route to these privileged structures starting from easily accessible 2-substituted pyridines and aryne precursors. A small library of compounds has been synthesized utilizing the developed method, affording variously substituted pyrido[1,2-a]indoles in moderate to good yields.     

Tantallaaziridines: from synthesis to catalytic applications

Tantallaaziridines are a class of organometallic compounds containing three-membered rings that include a tantalum, carbon and nitrogen atom. Closely related complexes containing the related iminoacyl ligand can be used as starting materials for tantallaaziridine synthesis. Tantallaaziridines can also be synthesized by reduction of imines or β-hydrogen abstraction of amides to give stable, isolable complexes. Tantallaaziridines possess a reactive Ta-C bond that can undergo stoichiometric transformations with unsaturated organic molecules to give new organometallic products. Upon quenching of such reactions with aqueous workup, selectively substituted small molecule amines can be prepared. Tantallaaziridines have also been proposed as catalytic intermediates in the direct α-alkylation of amines, hydroaminoalkylation, by exploiting the β-hydrogen abstraction route to regenerate the catalytically active species. Recent progress and remaining challenges in the field will be discussed.