Recent advances in radical‐mediated transformations of 1,3‐dienes

1,3‐Dienes are a class of easily accessible and versatile feedstock chemicals that can participate in a wide range of reactions to facilitate the synthesis of various valuable allylic compounds.In the past decades,radical methodology has emerged as a powerful tool for organic synthesis by virtue of the fact that diverse highly reactive radical species can usually be generated under mild,neutral and controlled conditions,and allow for rapid generation of molecular complexity.In this review,we critically illustrate the recent advances in the field of radical‐mediated transformations of 1,3‐dienes based on the different radical precursors and working modes.Wherever possible,particular emphasis is also put on the related mechanistic studies and synthetic applications.

NEW METHODS FOR AROMATIZATION OF STEROIDAL 2,5(10)-DIENES

New methods for dehydrogenation of steroidal 2,5(10)-dienes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or pyridinium hydrobromide perbromide(PHP,Py·HBr·Br_2) to aromatic A ring steroid in quantitative yield in short time are described.

The Addition Reaction of p-Chlorobenzaldoxime Dehydrodimer with 1,3-Dienes

The addition reaction of p chlorobenzaldoxime dehydrodimer and 1,3 dienes in refluxing chloroform gives linear 1,4 addition products. The reaction is probably a free radical process.

POLYMERIZATION MECHANISM OF DIENES WITH HOMOGENEOUS RARE EARTH CATALYSTS

The reaction mechanisms of diene polymerization with homogeneous rare earth catalyst are studied by means of the spectra of ~1H-NMR, one-and two-dimensions ^(13)C-NMR. Based on the data of above NMR spectra, it is proposed that the polymerization reaction proceeds according to the following mechanism: η~4-diene (cis-trans-)and η~3-allyl (syn-anti-).

Construction of remote cyano-substituted quaternary carbon centers via nickel-catalyzed migratory hydrocyanation of unconjugated dienes

The transition-metal-catalyzed migratory functionalization has emerged as a robust protocol for the building of C–C bonds remote from the“initiation”position.However,a similar strategy for the construction of quaternary carbon centers is still underdeveloped and only a limited number of reports exist.Herein,we report a nickel-catalyzed migratory hydrocyanation of unconjugated dienes to construct remote cyano-substituted quaternary carbon centers.This transformation features exceptional regioselectivity,mild reaction conditions,broad substrate scope and high yields.The synthetic utility of this method has been highlighted by a series of product derivatizations,and the potential of this transformation has been extended to synthesize TRPV1 antagonist and the key intermediate in the total synthesis of quebrachamine.Density functional theory(DFT)studies unveiled that the specific catalytic pocket assumed a significant role in the selective formation of cyano-substituted quaternary carbon centers.

Nickel-Catalyzed Regioselective Hydrosilylation of Conjugated Dienes

With the increasing demand for homoallylic silanes and allylic silanes,the highly efficient and regioselective hydrosilylations of conjugated dienes are urgently needed.Herein,we developed a Ni-catalyzed regiodivergent hydrosilylation of aromatic conjugated dienes by adjusting the temperature and ligands.Under low temperature(-30℃),an eternal-ligand-free system(Ni/t-BuOk)can efficiently facilitate the 3,4-anti-Markovnikov hydrosilylation to provide homoallylic silanes via electrophilic activation process;under room temperature(25℃),a ligand-controlled system(Ni/t-BuOk/PPh3)can eventuate the 3,4-Markovnikov hydrosilylation to produce allylic silanes via Chalk-Harrod process.Both systems are compatible with various conjugated dienes and primary silanes in excellent yields andregioselectivities.

Pd-Catalyzed Dienylation of Propargylic Esters Enabling Highly Stereoselective Synthesis of Danishefsky-Type Trisubstituted Dienes

The stereochemical synthesis of highly substituted Danishefsky-type dienes remains unsolved in organic chemistry.We describe a simple and efficient approach for the stereoselective synthesis of Danishefsky-type trisubstituted dienes from readily available propargylic esters via Pd-catalyzed dienylation reaction through the key intermediate metallacyclobutene in a regio-,chemo-and stereoselective fashion.This method facilitates a broad range of challenging trisubstituted dienes with a high level of stereocontrol.

Palladium-catalyzed 3,4-hydroaminocarbonylation of conjugated dienes for formation ofβ,γ-unsaturated amides

Hydrocarbonylation of conjugated dienes is one of the most promising yet challenging methods for the synthesis of carbonyl compounds.Herein,we reported the development of an unprecedented palladium-catalyzed branched selective 3,4-hydroaminocarbonylation of 1,3-dienes with CO and amines hydrochloride to affordβ,γ-unsaturated amides.This reaction employs readily available starting materials(including anilines,amines,amino acids,peptides,aryl-1,3-dienes,alyl-1,3-dienes)and tolerates a wide range of functional groups,thus providing a facile and effective approach to access a diverse array ofα-substitutedβ,γ-unsaturated amides.Mechanistic investigations suggested that the hydropalladation of dienes is irreversible,and the insertion of CO into the allyl-Pd species is probably the rate-limiting step.

Chiral Dienes: From Ligands to FLP Catalysts

Olefins are very easily accessible compounds which are both popular substrates in synthetic chemistry and good ligands in the organometallic complexes.This dual character makes olefins a rich source of chiral ligands and catalysts for asymmetric catalysis.Herein,we willbriefly summarize our studies on the development of chiral diene ligands for transition-metal catalyzed asymmetric reactions and chiral FLP catalysts for asymmetric metal-free hydrogenations and hydrosilylations.Several acyclic chiral diene ligands as well as P/olefin and S/olefin hybrid ligands were developed for Rh or Pd-catalyzed asymmetric reactions.With these ligands in hand,we further put forward a novel strategy for acquiring chiral FLP catalysts via the in situ hydroboration of chiral dienes with Piers'borane.These catalysts proved to be highly ffective for asymmetric metal-free hydrogenations and hydrosilylations of imines,ilyl enol ethers,ketones,and aromatic N-heterocycles.

Lanthanide complexes mediated coordinative chain transfer polymerization of conjugated dienes

Tremendous advances has been witnessed in the past few years in the lanthanide complexes mediated coordinative chain transfer polymerization(CCTP) of conjugated dienes. CCTP features catalyst economy, well-controlling over both microstructure and architecture of the resulting polymers, and accessibility for novel(co)polymers. This review highlights the recent progresses made in the field of CCTP of dienes. After a brief introduction, the body of this review is divided into three parts:(1) principle of CCTP;(2) coordinative chain transfer homopolymerization of dienes;(3) coordinative chain transfer copolymerization of dienes.At the end, we present some challenges remaining in this area and our personal opinion regarding where this field should continue to develop. CCTP represents a novel strategy to prepare polydiene synthetic rubbers with controlled high molecular weight and narrow molecular weight distribution, which has reached the practical industrial application level, demonstrating a great potential in industrialization.

Ligand controlled cobalt catalyzed regiodivergent 1,2-hydroboration of 1,3-dienes

Regiodivergent 1,2-hydroboration of 1,3-dienes with pinacolborane has been accomplished by well-defined cobalt complexes of different bidentate ligands. The iminopyridine-cobalt system is selective for Markovnikov 1,2-hydroboration to form allylboronates, while the FOXAP-cobalt(FOXAP=(S)-1-(diphenylphosphino)-2-[(S)-4-isopropyloxazolin-2-yl]ferrocene) catalyst effects the complementary anti-Markonikv 1,2-hydroboration to afford homoallyboronates with high regioselectivity.

Yttrium-catalyzed cis-1,4-Selective Polymerization of 2-(4-Halophenyl)-1,3-butadienes and Their Copolymerization with Isoprene

Polymerization of 2-(4-halophenyl)-1,3-butadiene(2-XPB) and their copolymerization with isoprene using a yttrium catalyst have been examined. The β-diketiminato yttrium bis(alkyl) complex(1) activated by [Ph_3 C][B(C_(6) F_(5))_(4)] and Ali Bu3 shows high cis-1,4-selectivity(>98%) for the polymerization of 2-XPB(2-XPB = 2-FPB, 2-Cl PB and 2-Br PB) to afford halogenated plastic poly(dienes) with glass transition temperatures of30–55 ℃. Moreover, the copolymerization of 2-XPB with isoprene(IP) has also been achieved by this catalyst, and the insertion ratios of 2-XPB can be facilely tuned in a full range of 0%–100% simply by changing the 2-XPB-to-IP ratio. Quantitative hydrogenation of cis-1,4-poly(2-XPB) results in perfect alternating ethylene-halostyrene copolymers, and an alternating copolymer of 4-vinylbenzoic acid with ethylene is obtained by a consecutive reaction of ethylene-4-bromostyrene copolymer with ^(n)Bu Li, CO_(2) and HCl.

SYNTHESIS AND CRYSTAL STRUCTURES OF THE BIMETALLIC RARE EARTH COMPLEXES AND STUDIES ON INSERTION MECHANISM OF DIENES POLYMERIZATION

The deepening of the studies on essentials of rare earth coordination catalyst brings about more and more reports on model compounds as active centre of the catalyst. Among them the most significant researches are those with identification of the crystal structures of compounds.

Phosphine-Catalyzed Annulations between Modified Allylic Derivatives and Polar Dienes and Substituent Effect on the Annulation Mode

in this work, the phosphine-catalyzed annulation reactions between modified allylic derivatives and polar 1,1-dicyano-1,3-dienes have been studied. In the catalysis of PPh3 （20 mol%）, a [4 ＋ 1 ] annulation reaction is realized between a series of l,l-dicyano-2,4-diaryl-1,3-dienes and ethoxycarbonyl-activated allylic acetate, producing polysubstituted cyclopentenes in modest to excellent yields. It is also observed that the substituents of both 1,3-dienes and allylic derivatives have a significant influence on the annulation mode： under the catalysis of PPh3 or PBu3 （20 mol%）, regioselective [3 ＋ 2] annulation products are formed from differently substituted substratcs.

Studies on sulfinatodehalogenation——ⅪⅩ.The reaction of perfluoroalkyl iodides and perfluoroalkane-sulfonyl bromides with conjugated dienes

The reaction of TbCl_3 with K[2,4-(CH_2)_2C_5H_5] at 0℃ in THF followed by crystalliza- tion at -90℃ led to a pale yellow hexagonal prismatic crystalline product [2,4-[CH_3)_2-η~5-C_5H_5]_(2-) Tb·1/2THF, which is highly sensitive to air and water and rapidly efflorescent at ambient temper- ature. The single Crystal X-ray diffraction data of the compound have been collected at low tem- perature (-60℃) and the crystal structure has been solved by heavy atom method. It belongs to triclinic system, space group Pl with lattice parameters a=8.477 (?),b=12.583 (?),c=12.858 (?), a=118.08°,β=91.38°,γ=108.75°,V=1120.36 (?)~ 3 and Z=2. Least-squares refinement converged to a final value R=0.043. The compound possesses an idealized G_(2h) symmetry、with three 2,4- dimethylpentadienyl ligands bound to the central terbium atom in a pentahapto mode (η~5). Each unit cell contains two molecules of[2,4-(CH_3)_2-η~5-C_5H_5]_3Tb and one molecule of solvent THF, of which the role in the lattice has been discussed in detail.

Rhodium-Catalyzed Defluorinative Vinylation of gem-Difluoroalkenes for the Synthesis of 2-Fluoro-1,3-dienes

Herein,we present a strategy for the formation of 2-fluoro-1,3-diene derivatives via rhodium-catalyzed direct C(sp2)-C(sp2) cross-coupling of gem-difluoroalkenes and acrylamides.By merging Rh(Ⅲ)-catalyzed C(sp2)-H bond activation and nucleophilic addition/F-elimination of gem-difluoroalkene,an efficient defluorinative vinylation reaction is uncovered,which leads to the generation of 2-fluoro-1,3-dienes in moderate to good yields with excellent stereoselectivity under mild conditions.Preliminary mechanistic study suggests unique effects of fluorine substituents which allow the reactivity profile not observed with the congeners bearing heavier halides.

Copolymers of Styrene with Conjugated Dienes by Titanium Catalysts:Synthesis,Characterization and Evaluation of the Mechanical Properties

1 Results Polymerization of butadiene,isoprene and styrene and binary copolymerization of styrene with butadiene and isoprene were investigated using the catalyst Ti(η5-C5H5)(η2-MBMP)Cl (1) (MBMP=2,2′-methylenebis(6-tert-butyl-4-methylphenoxo) activated with methylaluminoxane (MAO).Syndiotactic polystyrene, cis-1,4- polybutadiene and cis-1,4-polyisoprene were obtained in good yields at 50 °C.Binary copolymerization of styrene with butadiene yielded block copolymers containing segments of cis-1,4-polybut...

Nickel-Catalyzed Regio-and Enantioselective Hydroarylation of 1,3-Dienes with Indoles

The regio-and enantioselective functionalization of 1,3-dienes has become a powerful tool for the synthesis of allylic compounds,yet it remains a challenge for aliphatic dienes.Herein,we report a nickel-catalyzed asymmetric hydroarylation reaction of aliphatic and aromatic dienes with indoles to afford chiral indole derivatives.

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