Olefin‐Directed Palladium‐Catalyzed Regio‐ and Stereoselective Hydroboration of Allenes

An olefin‐directed palladium‐catalyzed regio‐ and stereoselective hydroboration of allenes has been developed to afford fully substituted alkenylboron compounds. The reaction showed a broad substrate scope: a number of functionalized allenes, including 2,3‐dienoate, 3,4‐dienoate, 3,4‐dienol, 1,2‐allenylphosphonate, and alkyl‐substituted allenes, could be used in this olefin‐directed allene hydroboration. The olefin unit was proven to be an indispensable element for this transformation.     

A Convergent Synthesis of Functionalized Alkenyl Halides through Cobalt(III)‐Catalyzed Three‐Component C−H Bond Addition

A Co^III‐catalyzed three‐component coupling of C(sp²)−H bonds, alkynes, and halogenating agents to give alkenyl halides is reported. This transformation proceeds with high regio‐ and diastereoselectivity, and is effective for a broad range of aryl and alkyl terminal alkynes. Diverse C−H bond partners also exhibit good reactivity for a range of heteroaryl and aryl systems as well as synthetically useful secondary and tertiary amide, urea, and pyrazole directing groups. This multicomponent transformation is also compatible with allenes in place of alkynes to furnish tetrasubstituted alkenyl halides, showcasing the first halo‐arylation of allenes.     

Transient‐Ligand‐Enabled ortho‐Arylation of Five‐Membered Heterocycles: Facile Access to Mechanochromic Materials

Reported herein is the first example of a direct arylation of heteroarenes by a transient‐ligand‐directed strategy without the need to construct and deconstruct the directing group. A wide range of heteroarenes undergoes the coupling with diverse aryl iodides to assemble a large library of highly selective and functionalized 3‐arylthiophene‐2‐carbaldehydes. This route provides an opportunity to rapidly access new mechanofluorochromic materials. Moreover, a novel strategy for mechanochromic luminogens with chromism trends of red‐ and blue‐shifts has been disclosed for the first time by facile functional‐group modifications to a common structural core.     

Palladium‐Catalyzed Coupling of Propargylic Alcohols with Boronic Acids under Ambient Conditions

A highly efficient palladium‐catalyzed direct coupling of propargylic alcohols with organoboronic acids to synthesize tri‐ and tetra‐substituted allenes has been developed under mild reaction conditions. Many useful functional groups are tolerated in this process with high to excellent yields. Preliminary biological studies showed that several tri‐ and tetra‐substituted allenes exhibited potent anti‐diabetic activities.     

Meeting the Challenge of Intermolecular Gold(I)‐Catalyzed Cycloadditions of Alkynes and Allenes

The development of gold(I)‐catalyzed intermolecular carbo‐ and hetero‐cycloadditions of alkynes and allenes has been more challenging than their intramolecular counterparts. Here we review, with a mechanistic perspective, the most fundamental intermolecular cycloadditions of alkynes and allenes with alkenes.     

Controlled Heterocyclization/Cross‐Coupling Domino Reaction of β,γ‐Allendiols and α‐Allenic Esters: Method and Mechanistic Insight for the Preparation of Functionalized Buta‐1,3‐dienyl Dihydropyrans

Starting from β,γ‐allendiols and α‐allenic acetates, a chemo‐ and regiocontrolled palladium‐catalyzed methodology has provided access to enantiopure 3,6‐dihydropyrans that bear a buta‐1,3‐dienyl moiety. Thus, it has been demonstrated for the first time that the preparation of six‐membered heterocycles through cross‐coupling reactions of two different allenes can be accomplished. These heterocyclization/cross‐coupling reactions have been developed experimentally and their mechanisms have additionally been investigated by a computational study.     

Rhodium‐Catalyzed Hydroformylation of 1,1‐Disubstituted Allenes Employing the Self‐Assembling 6‐DPPon System

A rhodium‐catalyzed hydroformylation of 1,1‐disubstituted allenes is reported. Using a Rh^I/6‐DPPon catalyst system, one can obtain β,γ‐unsaturated aldehydes in high regio‐ and chemoselectivity. The Z‐configured product is formed with up to >95 % selectivity when unsymmetrically 1,1‐disubstituted allenes are submitted to the reaction conditions. This is the first time that these interesting building blocks are accessible by hydroformylation of allenes. The utility of this methodology is demonstrated by further transformations of one of the obtained products.     

Perylene bisimide‐based semiconducting polymers: Synthesis via palladium‐catalyzed direct arylation,characterization, optoelectrical properties,and nanomorphology

Perylene bisimide (PBI)‐based acceptor polymers have been synthesized by the facile and environmental‐friendly palladium‐catalyzed direct arylation. The direct arylation using a bromothiophene‐extended PBI monomer, which was designed for the direct arylaion, proceeded to yield PBI‐based acceptor polymers (PPBI3T). As a result of screening the direct arylation conditions, PPBI3T with the number average molecular weight of 14,000 was successfully synthesized, and the spectroscopic and optoelectronic analysis demonstrated the synthesis of PPBI3T with the desired structure. The random compolymerization among naphthalene bisimide (NBI)‐based monomer, PBI‐based monomer, and 3,4‐dimethylthiophene afforded the random copolymers composed of NBI‐ and PBI‐based components (P(NBI3T‐PBI3T)). The composition of each component was controlled by changing the monomer feed ratio, and furthermore, the optical and electrochemical properties of P(NBI3T‐PBI3T) were also tunable by controlling the composition of each component. To the best of our knowledge, these results were the first accomplishment for the direct arylation synthesis of PBI‐based acceptor polymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3151–3158     

Allenyl‐β‐lactams: versatile scaffolds for the synthesis of heterocycles

The hybrid allenic β‐lactam moiety represents an excellent building block for carbo‐ and heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under thermal and radical‐induced conditions. More recently, the use of transition‐metal catalysis has been introduced as an alternative that relies on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of bi‐ and tricyclic compounds in a regio‐ and stereoselective manner. This overview focuses on the most recently developed cyclizations on 2‐azetidinone‐tethered allenes along with remarkable early works accounting for the mechanism, as well as for the regio‐ and diastereoselectivities of the cyclizations. DOI 10.1002/tcr.201100011     

Rhodium‐Catalyzed Cross‐Cyclotrimerization and Dimerization of Allenes with Alkynes

It has been established that a cationic rhodium(I)/binap complex catalyzes the cross‐cyclotrimerization of two molecules of a monosubstituted allene with one molecule of a functionalized alkyne to give 3,6‐dialkylidenecyclohex‐1‐enes. In contrast, the reactions involving di‐ or trisubstituted allenes and/or unfunctionalized alkynes afforded cross‐dimerization products, substituted dendralenes, through β‐hydrogen elimination from the corresponding rhodacycles.     

Highly Selective Construction of Seven‐Membered Carbocycles by Olefin‐Assisted Palladium‐Catalyzed Oxidative Carbocyclization–Alkoxycarbonylation of Bisallenes

An olefin‐assisted palladium‐catalyzed oxidative carbocyclization–alkoxycarbonylation of bisallenes to afford seven‐membered carbocycles has been established. This dehydrogenative coupling reaction showed excellent substrate scope and functional group compatibility. The reaction exhibited high chemo‐ and regioselectivity, and ester 3 was the only product obtained. The olefin unit has been proven to be indispensable during the reaction. Moreover, intramolecular oxidative coupling suggests that the reaction proceeds via a (π‐allyl)palladium intermediate.     

Chiral Phosphorus–Olefin Ligands for the RhI‐Catalyzed Asymmetric Addition of Aryl Boronic Acids to Electron‐Deficient Olefins

New chiral phosphorus–olefin hybrid ligands derived from the rigid “privileged” l ‐proline have been conveniently prepared and applied in the rhodium‐catalyzed asymmetric arylation of electron‐deficient olefins with arylboronic acids at room temperature; this reaction provides the desired products in excellent yields and high enantioselectivities. The origin of observed stereoselectivity has been investigated by density functional theory (DFT) calculations.     

Rhodium(III)‐Catalyzed [4+1] Annulation of Aromatic and Vinylic Carboxylic Acids with Allenes: An Efficient Method Towards Vinyl‐Substituted Phthalides and 2‐Furanones

A highly regio‐ and stereoselective synthesis of 3,3‐disubstituted phthalides from aryl carboxylic acids and allenes using a rhodium(III) catalyst has been demonstrated. The reaction features broad functional group tolerance and provides a simple and straightforward route to the synthesis of various 3‐vinyl‐substituted phthalides. Furthermore, the catalytic reaction can also be applied to the synthesis of biologically active 5‐vinyl‐substituted 2‐furanones from α,β‐unsaturated carboxylic acids and allenes. The reactions proceed through a carboxylate‐assisted ortho‐C?H activation and [4+1] annulation. The preliminary mechanistic studies suggest that a C?H cleavage is the rate‐determining step.     

Base‐Selective Five‐ versus Six‐Membered Ring Annulation in Palladium‐Catalyzed C–C Coupling Cascade Reactions: New Access to Electron‐Poor Polycyclic Aromatic Dicarboximides

Palladium‐catalyzed base‐selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross‐coupling and direct C−H arylation afforded a series of new five‐ and six‐membered ring annulated electron‐poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs₂CO₃) as auxiliary base in these C−C coupling cascade reactions led exclusively to six‐membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five‐membered ring annulated products. This base‐dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X‐ray analysis of the respective five‐ and six‐membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry.     

Synthesis of 3‐Aryl/methoxycarbonyl‐3,4‐dihydroisocoumarin‐6‐carboxylic Acid Derivatives

3‐Substituted methyl 3,4‐dihydroisocoumarin‐6‐carboxylates were obtained by the intramolecular cyclization of 2,5‐dimethoxycarbonyl benzenediazonium bromides with methyl/ethyl acrylate and styrenes under Meerwein's arylation conditions.     

Rhodium‐Catalyzed Dynamic Kinetic Asymmetric Allylation of Phenols and 2‐Hydroxypyridines

Inspired by the mechanistic studies of rhodium‐catalyzed atom‐economic addition of carboxylate acids to allenes, a rhodium‐catalyzed dynamic kinetic asymmetric allylation of different nucleophiles with racemic allylic carbonates has been developed. High regio‐ and enantioselectivities can be obtained under neutral conditions and, furthermore, the chemoselectivities can be controlled by different diphosphine ligands. (R,R)‐QuinoxP* leads to selective O‐allylation of phenols, whereas when embedding (S,S)‐DIOP as the ligand, 2‐naphthol is ortho‐C‐allylated for the first time in high enantioselectivity. To this end, hydroxypyridines can be N‐allylated by Rh^I/(S)‐DTBM‐Segphos via the same intermediate as in the previously reported atom‐economic addition to allenes.     

The Photoredox‐Catalyzed Meerwein Addition Reaction: Intermolecular Amino‐Arylation of Alkenes

A variety of amides are efficiently accessible under mild conditions by intermolecular amino‐arylation using a photo Meerwein addition with visible light. The reaction has a broad substrate scope, tolerates a large range of functional groups, and was applied to the synthesis of a 3‐aryl‐3,4‐dihydroisoquinoline.     

Catalytic Enantioselective Synthesis of a 3‐Aryl‐3‐benzyloxindole (=3‐Aryl‐3‐benzyl‐1,3‐dihydro‐2H‐indol‐2‐one) Exhibiting Antitumor Activity

A palladium‐catalyzed intramolecular α‐arylation of an amide in the presence of a bulky chiral N‐heterocyclic carbene ligand is the key step in the first catalytic synthesis of (3R)‐6‐chloro‐3‐(3‐chlorobenzyl)‐1,3‐dihydro‐3‐(3‐methoxyphenyl)‐2H‐indol‐2‐one ((R)‐ 5 ). This oxindole, in racemic form, had been shown previously to be an anticancer agent. (R)‐ 5 was obtained with an overall yield of 45% and with 96% enantioselectivity.     

Tandem IBX‐Promoted Primary Alcohol Oxidation/Opening of Intermediate β,γ‐Diolcarbonate Aldehydes to (E)‐γ‐Hydroxy‐α,β‐enals

A tandem IBX‐promoted oxidation of primary alcohol to aldehyde and opening of intermediate β,γ‐diolcarbonate aldehyde to (E)‐γ‐hydroxy‐α,β‐enal has been developed. Remarkably, the carbonate opening delivered exclusively (E)‐olefin and no over‐oxidation of γ‐hydroxy was observed. The method developed has been extended to complete the stereoselective total synthesis of both (S)‐ and (R)‐coriolides and d ‐xylo‐ and d ‐arabino‐C‐20 guggultetrols.     

A Versatile Room‐Temperature Route to Di‐ and Trisubstituted Allenes Using Flow‐Generated Diazo Compounds

A copper‐catalyzed coupling reaction between flow‐generated unstabilized diazo compounds and terminal alkynes provides di‐ and trisubstituted allenes. This extremely mild and rapid transformation is highly tolerant of several functional groups.