1,7-Octadiene-Assisted Tandem Multicomponent Cross-Enyne Metathesis (CEYM)-Diels-Alder Reactions: A Useful Alternative to Mori's Conditions

The use of 1,7-octadiene as an in situ source of ethylene led us to develop a novel multicomponent tandem cross-enyne metathesis (CEYM)-Diels-Alder reaction. The process can be considered a relay metathesis, in which the ethylene liberated in the ring-closing metathesis (RCM) of 1,7-octadiene initiates the tandem sequence. Aliphatic, aromatic, and fluorinated alkynes and several dienophiles are compatible with the process, which is particularly efficient with aromatic alkynes. This methodology constitutes a useful variant of Mori's conditions in CEYM-related reactions.     

Unique Insertion Mode of 1,7‐Octadiene in Copolymerization with Ethylene by a Constrained‐Geometry Catalyst

Summary: The copolymerization of ethylene and 1,7‐octadiene (OD) was investigated with a constrained‐geometry catalyst. The ¹³C NMR spectrum of the copolymer indicated cyclization insertion of the OD unit in the penultimate position after a single ethylene insertion step. This unique insertion mode of OD forms a 1,5‐disubstituted cyclononane unit in the main chain of polyethylene.

Copolymerization of ethylene and 1,7‐octadiene (OD) with a constrained‐geometry catalyst.     

Long‐chain‐branched polyethene by the copolymerization of ethene and nonconjugated α,ω‐dienes

Ethene was copolymerized (1) with 1,5‐hexadiene with rac‐ethylenebis(indenyl)zirconium dichloride/methylaluminoxane (MAO) used as a catalyst and (2) with 1,7‐octadiene with bis(n‐butylcyclopentadienyl)zirconium dichloride/MAO and rac‐ethylenebis(indenyl)hafnium dichloride (Et[Ind]₂HfCl₂)/MAO used as catalysts at 80 °C in toluene. The copolymer microstructure and the influence of diene incorporation on the rheological properties were examined. Ethene and 1,5‐hexadiene formed a copolymer in which a major fraction of the 1,5‐hexadiene was incorporated into rings and a small fraction formed 1‐butenyl branches. The copolymerization of ethene with 1,7‐octadiene resulted in a higher selectivity toward branch formation. Some of the branches formed long‐chain‐branching (LCB) structures. The ring formation selectivity increased with decreasing ethene concentration in the polymerization reactor. Melt rheological properties of the diene copolymers resembled those of metallocene‐catalyzed LCB homopolyethenes and depended on the vinyl content, the catalyst, and the polymerization conditions. At high diene contents, all three catalysts produced crosslinked polyethene. This was especially pronounced with Et[Ind]₂HfCl₂, where only 0.2 mol % 1,7‐octadiene in the copolymer was required to achieve significantly modified rheological properties. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3805–3817, 2001     

Tandem Three‐Component Synthesis of syn‐1,2‐ and syn‐1,3‐Diol Derivatives

The development of efficient methods for stereocontrolled synthesis of polyol derivatives has been of continuing interest for the synthetic community. We describe herein tandem olefin cross‐metathesis/hemiacetalization/intramolecular oxa‐Michael addition of allylic/homoallylic alcohols, α,β‐unsaturated ketones, and aldehydes, which enabled the synthesis of syn‐1,2‐ and syn‐1,3‐diol derivatives in a step‐economical manner. A series of differentially protected polyol derivatives could be obtained in subsequent transformations via chemoselective/regioselective cleavage of the acetal moiety of the tandem reaction products.     

Copper‐Catalyzed Difunctionalization of Activated Alkynes by Radical Oxidation–Tandem Cyclization/Dearomatization to Synthesize 3‐Trifluoromethyl Spiro[4.5]trienones

A copper‐catalyzed difunctionalizing trifluoromethylation of activated alkynes with the cheap reagent sodium trifluoromethanesulfinate (NaSO₂CF₃ or Langlois’ reagent) has been developed incorporating a tandem cyclization/dearomatization process. This strategy affords a straightforward route to synthesis of 3‐(trifluoromethyl)‐spiro[4.5]trienones, and presents an example of difunctionalization of alkynes for simultaneous formation of two carbon–carbon single bonds and one carbon–oxygen double bond.     

Palladium‐Catalyzed Regioselective Aromatic Extension of Internal Alkynes through a Norbornene‐Controlled Reaction Sequence

A regioselective aromatic π‐extension reaction of internal alkynes is reported. The proposed method employs three easily available components, namely aryl halides, 2‐haloarylcarboxylic acids, and disubstituted acetylenes. The transformation is driven by a controlled reaction sequence of C?H activation, decarboxylation, and annulation to give poly(hetero)aromatic compounds in a site‐selective fashion. Unlike in previously reported palladium‐catalyzed three‐component annulations, alkyne carbopalladation is the last step of this tandem reaction.     

Preparation of novel,liquid, solvent‐free,polyolefin‐based adhesives

An innovative procedure for functionalization of polyolefins was developed. It was found that synthesized polyolefins end‐capped with trimethoxysilane (silylated polyolefins) are new polyolefin‐based adhesives. To prepare the mentioned materials,1‐octene as a higher α‐olefin was cooligomerized with two linear, nonconjugated dienes (ie, 1,5‐hexadiene and 1,7‐octadiene) by using metallocene catalyst system, Cp₂HfCl₂/MAO, at room temperature. Then, amine‐terminated trimethoxysilane (3‐aminopropyltrimethoxysilane) was reacted with unsaturated bonds of synthesized cooligomers in the presence of palladium(II) acetate. Embedding of the dienes on 1‐octene oligomeric chains was explored by Fourier transform infrared (FTIR), ¹H, and ¹³C‐NMR spectroscopy. On the basis of the results, 1,5‐hexadiene showed both 1‐butene branch and five‐member ring. On the other hand, 1,7‐octadiene was incorporated by 1,2‐addition, forming both 1‐hexene branch and seven‐member ring in the cooligomer backbone. Mole percentage of C?C and cyclic moieties reached to a value of 28.54, 18.59% mol in 1‐octene/1,5‐hexadiene, and 38.04, 6.71% mol in 1‐octene/1,7‐octadiene cooligomers, respectively. Reaction of synthesized cooligomers with 3‐aminopropyltrimethoxysilane was confirmed by FTIR spectroscopy, which yielded targeted adhesives. To study the adhesion properties, resulting adhesives were applied to different substrates. Obtained results demonstrated that tensile shear strength of synthesized adhesives to polar substrates was 2.21% to 2.84% more than nonpolar substrates. Among studied systems, the best performance was achieved by1‐octene/1,7‐octadiene–based adhesive and Al substrate with tensile shear strength of 1.45 N/mm².     

Ring‐Closing Olefin Metathesis for the Synthesis of Benzene Derivatives

Benzene derivatives were synthesized in excellent yield from 1,4,7‐trien‐3‐ols by tandem ruthenium‐catalyzed ring‐closing olefin metathesis (RCM)/dehydration. The method was extended to the tandem RCM/oxidation process to obtain phenol and aniline derivatives. This method displays many advantages over aromatic‐substitution‐based classical routes.     

Insertion of Isolated Alkynes into Carbon–Carbon σ‐Bonds of Unstrained Cyclic β‐Ketoesters via Transition‐Metal‐Free Tandem Reactions: Synthesis of Medium‐Sized Ring Compounds

The transition‐metal‐free insertion of isolated alkynes into carbon–carbon σ‐bonds of unstrained cyclic β‐dicarbonyl compounds has been reported. These tandem reactions offer an efficient synthesis of medium‐sized ring or fused‐ring compounds through ring expansion. The methodology has the potential to be widely used throughout organic synthesis due to the easily accessible starting materials and mild reaction conditions.     

Heteroacene Synthesis through C−S Cross‐Coupling/5‐endo‐dig Cyclization

Highly efficient, one‐step synthesis of sulfur‐containing heteroacenes was achieved through palladium‐catalyzed C?S cross‐coupling of bis‐alkynes with thioacetate as hydrogen sulfide surrogate. Heteroacenes consisting of three, five, and seven fused aromatic rings were obtained in a single catalytic step by four‐, six‐, and eightfold C?S bond formation.     

The First Stereoselective Total Synthesis of a Naturally Occurring Bioactive Diarylheptanoid, (3R,6E)‐1,7‐Bis(4‐hydroxyphenyl)hept‐6‐en‐3‐ol,through Two Different Approaches

The stereoselective total synthesis of a naturally occurring bioactive diarylheptanoid, (3R,6E)‐1,7‐bis(4‐hydroxyphenyl)hept‐6‐en‐3‐ol, has been accomplished starting from 4‐hydroxybenzaldehyde through two different approaches involving Wittig olefination, hydrolytic kinetic resolution of a racemic epoxide, and olefin cross‐metathesis reaction as the key steps.     

Rhodium(III)‐Catalyzed Three‐Component Reaction of Imines,Alkynes, and Aldehydes through CH Activation

An efficient rhodium(III)‐catalyzed tandem three‐component reaction of imines, alkynes and aldehydes through C?H activation has been developed. High stereo‐ and regioselectivity, as well as good yields were obtained in most cases. The simple and atom‐economical approach offers a broad scope of substrates, providing polycyclic skeletons with potential biological properties.     

Hypervalent Iodine(III)‐Mediated Benzannulation of Enamines with Alkynes: an Efficient Synthesis of Substituted Aminonaphthoic Acid Derivatives

An intermolecular two C? C bond formation procedure for the synthesis of carbocycles mediated by hypervalent iodine(III) reagents was developed. This metal free protocol provided a new approach for the synthesis of useful substituted 1‐amino‐2‐naphthoic acid derivatives via benzannulation reactions. Various N‐unsubstituted and N‐alkyl substituted aromatic enamines with terminal alkynes and non‐terminal alkynes can be converted into corresponding 1‐amino‐2‐naphthoic acid derivatives under mild reaction conditions. When meta‐substituted phenyl enamines were employed in the reaction, two cyclization paths were detected in the reaction and ortho‐cyclization products were the only or major products. Good functional group tolerance, readily available material and high atom utilization efficiency make this method a potential procedure which may find broad application in organic synthesis.     

Tandem Z‐Selective Cross‐Metathesis/Dihydroxylation: Synthesis of anti‐1,2‐Diols

A stereoselective synthesis of anti‐1,2‐diols has been developed using a multitasking Ru catalyst in an assisted tandem catalysis protocol. A cyclometalated Ru complex catalyzes first a Z‐selective cross‐metathesis of two terminal olefins, followed by a stereospecific dihydroxylation. Both steps are catalyzed by Ru, as the Ru complex is converted to a dihydroxylation catalyst upon addition of NaIO₄. A variety of olefins were transformed into valuable, highly functionalized, and stereodefined molecules. Mechanistic experiments were performed to probe the nature of the oxidation step and catalyst inhibition pathways. These experiments point the way to more broadly applicable tandem catalytic transformations.     

Side‐Chain Modification and “Grafting Onto” via Olefin Cross‐Metathesis

Olefin cross‐metathesis is introduced as a versatile polymer side‐chain modification technique. The reaction of a poly(2‐oxazoline) featuring terminal double bonds in the side chains with a variety of functional acrylates has been successfully performed in the presence of Hoveyda–Grubbs second‐generation catalyst. Self‐metathesis, which would lead to polymer–polymer coupling, can be avoided by using an excess of the cross‐metathesis partner and a catalyst loading of 5 mol%. The results suggest that bulky acrylates reduce chain–chain coupling due to self‐metathesis. Moreover, different functional groups such as alkyl chains, hydroxyl, and allyl acetate groups, as well as an oligomeric poly(ethylene glycol) and a perfluorinated alkyl chain have been grafted with quantitative conversions.     

Ring‐Rearrangement Metathesis

Ring‐rearrangement metathesis (RRM) refers to the combination of several metathesis transformations into a domino process, in which an endocyclic double bond of a cycloolefin reacts with an exocyclic alkene. RRM has proven to be a powerful method for the rapid construction of complex structures. The extension of the basic ring‐opening–ring‐closing metathesis process by further metathesis steps as well as an examination of the driving forces, limits, scope, recent advantages, and future perspectives of these domino sequences is presented with various examples, thus reflecting the high efficiency and utility of RRM in organic synthesis.     

Facile Installation of 2‐Reverse Prenyl Functionality into Indoles by a Tandem N‐Alkylation–Aza‐Cope Rearrangement Reaction and Its Application in Synthesis

An unprecedented tandem N‐alkylation–ionic aza‐Cope (or Claisen) rearrangement–hydrolysis reaction of readily available indolyl bromides with enamines is described. Due to the complicated nature of the two processes, an operationally simple N‐alkylation and subsequent microwave‐irradiated ionic aza‐Cope rearrangement–hydrolysis process has been uncovered. The tandem reaction serves as a powerful approach to the preparation of synthetically and biologically important, but challenging, 2‐reverse quaternary‐centered prenylated indoles with high efficiency. Notably, unusual nonaromatic 3‐methylene‐2,3‐dihydro‐1H‐indole architectures, instead of aromatic indoles, are produced. Furthermore, the aza‐Cope rearrangement reaction proceeds highly regioselectively to give the quaternary‐centered reverse prenyl functionality, which often produces a mixture of two regioisomers by reported methods. The synthetic value of the resulting nonaromatic 3‐methylene‐2,3‐dihydro‐1H‐indole architectures has been demonstrated as versatile building blocks in the efficient synthesis of structurally diverse 2‐reverse prenylated indoles, such as indolines, indole‐fused sultams and lactams, and the natural product bruceolline D.     

Metal‐Free σ‐Bond Metathesis in 1,3,2‐Diazaphospholene‐Catalyzed Hydroboration of Carbonyl Compounds

The first metal‐free catalytic hydroboration of carbonyl derivatives has been developed in which a catalytic amount of 1,3,2‐diazaphospholene effectively promotes a hydroboration reaction of aliphatic and aromatic aldehydes and ketones. The reaction mechanism involves the cleavage of both the P? O bond of the alkoxyphosphine intermediate and the B? H bond of pinacolborane as well as the formation of P? H and B? O bonds. Thus, the reaction proceeds through a non‐metal σ‐bond metathesis. Kinetic and computational studies suggest that the σ‐bond metathesis occurred in a stepwise but nearly concerted manner.     

Silica Sulfuric Acid‐Catalyzed One‐Pot Synthesis,Mechanism, and Fluorescence Properties of 2‐(2‐arylquinolin‐4‐(1H)‐ylidene)malononitriles

A mild, one‐pot synthesis of 2‐(2‐arylquinolin‐4‐(1H)‐ylidene)malononitriles is developed via the silica sulfuric acid‐catalyzed tandem condensation of 2‐aminoacetophenone with malononitrile and aromatic aldehyde in ionic liquid. It is proposed that malononitrile acted as not only a reactant but also a promoter in the interesting process. The fluorescence properties screening showed a new compound has high fluorescence quantum yield.     

Synthesis of Unsymmetrical 1,3‐Diynes via Pd/Cu‐Catalyzed Cross‐Coupling of Terminal Alkynes at Room Temperature

A facile and practical synthetic route of unsymmetrical 1,3‐diynes via the PdCl/CuI catalyzed oxidative coupling of two different terminal alkynes has been developed by using 3‐(diphenylphosphino)propanoic acid as a ligand in the presence of oxygen. This system is suitable for not only aromatic alkynes but also heteroaromatic and aliphatic alkynes which were transformed into the corresponding unsymmetrical 1,3‐diynes in moderate to good yields at room temperature. Moreover, the unsymmetrical 1,3‐diynes were also obtained on a multi‐gram scale. Mechanistic studies suggest that oxygen plays a key role in the catalytic cycles.