Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes

Advances in the palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes are presented according to substrate types and chiral monophosphine ligands. Chiral monodentate phosphine ligands with a binaphthyl moiety have been proven to be the most efficient ligands for cyclic 1,3-dienes, and planar chiral ferrocenylmonophosphine ligands with two ferrocenyl moieties for linear 1,3-dienes. The ferrocenylmonophosphine ligands have expanded the substrate scope to 1,3-enynes in the asymmetric hydrosilylation. Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes and 1,3-enynes leads to the stereoselective synthesis of allylsilanes and allenylsilanes, respectively.     

Regiodivergent sulfonylarylation of 1,3-enynes via nickel/photoredox dual catalysis

Catalytic difunctionalization of 1,3-enynes represents an efficient and versatile approach to rapidly assemble multifunctional propargylic compounds, allenes and 1,3-dienes. Controlling selectivity in such addition reactions has been a long-standing challenging task due to multiple reactive centers resulting from the conjugated structure of 1,3-enynes. Herein, we present a straightforward method for regiodivergent sulfonylarylation of 1,3-enynes via dual nickel and photoredox catalysis. Hinging on the nature of 1,3-enynes, diverse reaction pathways are feasible: synthesis of α-allenyl sulfones via 1,4-sulfonylarylation, or preparation of (E)-1,3-dienyl sulfones with high chemo-, regio- and stereoselectivity through 3,4-sulfonylarylation. Notably, this is the first example that nickel and photoredox catalysis are merged to achieve efficient and versatile difunctionalization of 1,3-enynes.

A mild reaction protocol for regiodivergent sulfonylarylation of 1,3-enynes via dual nickel and photoredox catalysis has been developed, which led to efficient synthesis of α-allenyl sulfones or 1,3-dienyl sulfones.     

Catalytic enantioselective halolactonization of enynes and alkenes

New organocatalysts have been developed for the enantioselective halolactonization of (Z)-1,3-enynes and 1,1-disubstituted alkenes. In the case of 1,3-enynes, the carboxylate nucleophile and halogen electrophile were added to the conjugated π-system from the same face. Up to 99% ee was achieved for the 1,4-syn-bromolactonization of conjugated (Z)-1,3-enynes. Based on the results from the enyne halolactonization, a second generation of catalysts was designed for simple olefins. Up to 91% ee was observed for chlorolactonization of 1,1-disubstituted alkenes. The catalysts developed for the enantioselective halolactonization of both enynes and alkenes are composed of a cinchona alkaloid skeleton tethered to a urea group.     

Metalation reactions—VIII Metalation of 1,4-enynes and protonation of their anions

A series of 1,4-enynes was prepared and the compounds metalated with butyllithium in ether. The formation of the mono- and dilithio derivatives was studied by PMR and UV. Protonation of the dilithio compounds gave vinylallenes, 1,3- and 1,4-enynes. Isomerisation of the 1,4-enynes in DMSO using dimsylsodium gave vinylacetylenes from compounds containing a terminal double bond and vinylallenes from those with an internal double bond. The sequence of the H—D exchange of the various protons was also studied.     

Silaborations of 1,3-enynes - substrate controlled allene/1,3-diene selectivity

Silaboration of 1,3-enynes catalyzed by group 10 metal complexes affords 1,3-dienes with vinylborane and vinylsilane functions or 1,2-dienes with allylborane and vinylsilane functions. The type of product formed is determined by the size of the alkyne substituent.     

Enantioselective Synthesis of Multisubstituted Allenes by Cooperative Cu/Pd-Catalyzed 1,4-Arylboration of 1,3-Enynes

A cooperative Cu/Pd-catalyzed enantioselective synthesis of multisubstituted allenes is established. By employing chiral sulfoxide phosphine (SOP)/Cu and PdCl₂(dppf) complexes as catalysts, the 1,4-arylboration of 1,3-enynes provides an efficient approach to trisubstituted chiral allenes with up to 92 % yield and 97:3 er. Furthermore, by using 2-substituted 1,3-enynes as substrates, the tetrasubstituted chiral allenes were successfully generated using this strategy. Finally, theoretical calculations indicate that the transmetallation of the allenylcopper species is the rate-limiting step of this transformation.     

Synthesis of 1,3-enynes via Suzuki-type reaction of vinylic tellurides and potassium alkynyltrifluoroborate salts

The palladium-catalyzed cross-coupling reaction between potassium alkynyltrifluoroborate salts and vinylic tellurides proceeds readily to afford 1,3-enynes with moderate to good yields.     

Gold(I)-catalyzed intermolecular addition of carbon nucleophiles to 1,5- and 1,6-enynes

Gold(I)-catalyzed addition of carbon nucleophiles to 1,6-enynes gives two different type of products by reaction at the cyclopropane or at the carbene carbons of the intermediate cyclopropyl gold carbenes. The 5-exo-dig cyclization is followed by most 1,6-enynes, although those bearing internal alkynes and alkenes react by the 6-endo-dig pathway. The cyclopropane versus carbene site-selectivity can be controlled in some cases by the ligand on the gold catalyst. In addition to electron-rich arenes and heteroarenes, allylsilanes and 1,3-dicarbonyl compounds can be used as the nucleophiles. In the reaction of 1,5-enynes with carbon nucleophiles, the 5-endo-dig pathway is preferred.     

Synthesis of 1,3,5-trisubstituted pyrazolines via Zn(II)-catalyzed double hydroamination of enynes with aryl hydrazines

An efficient Zn(II)-catalyzed intermolecular double hydroamination of 1,3-enynes with aryl hydrazines, for the synthesis of pyrazolines, has been discussed.     

Au- and pt-catalyzed cycloisomerizations of 1,5-enynes to cyclohexadienes with a broad alkyne scope

We describe the development of gold- and platinum-catalyzed cycloisomerizations of 1,5-enynes. This catalytic process displays a wide alkyne scope and furnishes a range of highly functionalized 1,4- and 1,3-cyclohexadienes. In the case of 1-siloxy-1-yne-5-enes, the reactions are efficiently catalyzed by AuCl (1 mol %) at ambient temperature to afford siloxy cyclohexadienes or the corresponding 1,2- and 1,3-cyclohexenones upon subsequent protodesilylation. We propose that the reaction proceeds via a novel mechanism involving a series of 1,2-alkyl shifts. Elucidation of this unusual reaction mechanism enabled us, in turn, to significantly expand the scope of the cycloisomerization by incorporation of a quaternary center at the C(3) position of the enyne. Indeed, we established that PtCl(2) (5 mol %) efficiently catalyzed the cycloisomerizations of 1,5-enynes containing terminal, internal, and arene-conjugated alkynes. Since a variety of 1,5-enynes are readily accessible, the cycloisomerization provides a rapid approach to a wide range of highy substituted cyclohexadienes for many subsequent synthetic applications.     

Stereoselective Synthesis of Functionalized 1,3-Enynes through Recyclable Copper(I)-Catalyzed Three-Component Reaction of Terminal Alkynes,Diazoesters and Aldehydes

A highly efficient heterogeneous copper(I)-catalyzed three-component coupling of terminal alkynes, diazoesters and aldehydes has been achieved by using 10 mol% of copper(I) iodide complex [N,N-CuI-MCM-41] anchored on 2-aminoethylamino-modified mesoporous material MCM-41 as the catalyst under mild conditions, delivering a wide variety of 2-alkoxycarbonyl-substituted (E)-1,3-enynes in mostly good to high yields with excellent stereoselectivity. The heterogenized copper(I) complex can be facilely prepared from inexpensive reagents by using a simple procedure and exhibits a remarkably higher catalytic activity than CuI, and can be recycled more than ten times without a significant drop in its catalytic efficiency. This protocol represents the first example of heterogeneous copper-catalyzed stereoselective construction of functionalized 1,3-enynes from simple and commercially available starting materials.     

Palladium-catalyzed one-pot construction of difluorinated 1,3-enynes from α,α,α-iododifluoroacetones and alkynes

A palladium-catalyzed one-pot difunctionalization of alkynes with α,α,α-iododifluoroacetones is introduced for the synthesis of difluorinated 1,3-enynes. The reaction proceeds through the radical addition of RCOCF₂ radical to alkynes and subsequent Sonogashira coupling with the same alkynes to give the 1,3-enyne products with high regio and stereoselectivity.     

Rhodium-catalyzed carbonylation of 3-acyloxy-1,4-enynes for the synthesis of cyclopentenones

Functionalized cyclopentenones were synthesized by a Rh-catalyzed carbonylation of 3-acyloxy-1,4-enynes, derived from alkynes and α,β-unsaturated aldehydes. The reaction involved a Saucy-Marbet 1,3-acyloxy migration of propargyl esters and a [4 + 1] cycloaddition of the resulting acyloxy substituted vinylallene with CO.     

Reactions of benzimidazole-2-thiol with N-alkyl-1-aza-1,3-enynes

Reactions of N-alkyl-1-aza-1,3-enynes with benzimidazole-2-thiol in anhydrous dimethylformamide have been studied. The structure of the obtained compounds has been elucidated from the NMR data.     

Facile Construction of Furanoacenes by a Three-Step Sequence Going through Disilyl-exo-cyclic Dienes

Facile synthesis of various benzonaphthofurans was achieved by intramolecular hydroarylation of 1,4-disilyl-2-aryloxy-1,3-enynes followed by cycloaddition with arynes or alkenes and finally desilylaromatization. The three-step transformation can be operated sequentially in one-pot, providing with a range of furanoacenes easily and highly effectively.     

Visible-light-induced,autopromoted nickel-catalyzed three-component arylsulfonation of 1,3-enynes and mechanistic insights

A light-induced, nickel-catalyzed three-component arylsulfonation of 1,3-enynes in the absence of photocatalyst is reported.This methodology exhibited mild conditions, broad scope and high efficiency, and its synthetic utility has been demonstrated by a concise total synthesis of sulfone-containing drug molecule. Detailed mechanistic studies indicated that this light induced nickel catalysis is autopromoted by in situ produced allene, which plays a key role as co-ligand in the photoactive excite...     

3,3,3-trichloropropyl-1-triphenylphosphorane: a reagent for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes

3,3,3-Trichloropropyl-1-triphenylphosphonium chloride is conveniently prepared from 2-chloroethanol, triphenylphosphine, and trichloroacetic acid. Deprotonation of this reagent generates 3,3,3-trichloropropyl-1-triphenylphosphorane, which reacts with aldehydes to give trichloromethylated (Z)-olefins, which are useful for the synthesis of (Z)-1,3-enynes, (Z,Z)-1-chloro-1,3-dienes, and 1,3-diynes in high yields and stereospecificities.     

Group 14 Elements Hetero-Difunctionalizations via Nickel-Catalyzed Electroreductive Cross-Coupling

The difunctionalization of unsaturated bonds plays a vital role in the enrichment of molecular complexity. While various catalytic methods for alkene and alkyne difunctionalization have been developed in recent years, hetero-functionalization the introduction of two different atoms has been less explored. This is mainly due to the challenges associated with achieving high chemo-, regio-, and stereoselectivity, especially when adding two similar atoms from the same group across unsaturated bonds. In this study, we describe a nickel-catalyzed, three-component reductive protocol for group 14 element hetero-difunctionalization of 1,3-enynes using electrochemistry. This new method is mild, selective, and general, allowing for the silyl-, germanyl-, and stannyl-alkylation of enynes. Various chlorosilanes as well as chlorogermans, and chlorostannanes can be successfully used in combination with aryl/alkyl-substituted 1,3-enynes and primary, secondary, and tertiary alkyl bromides in the electroreductive coupling.     

A Convenient and Efficient Route to 1,4-Bis（heteroaryl）-buta-1,3-diene and 4-Heteroarylbut-1-en-3-yne from 1,4-Dichlorobut-2-yne

A convenient and practical route to functionalized conjugated 1,3-enynes and 1,3-dienes is described. 1,4-Bis（heteroaryl）- 1,3-diene and 1-heteroarylbut- 1-en-3-yne derivatives were prepared from 1,4-dichloro-2-butyne and corresponding N-heteroarenes such as imidazole, pyrrole, pyrazole and indole derivatives in the presence of bases in good to high yields.     

Facile Stereoselective Synthesis of (E)-1-Arylseleno-Substituted 1,3-Enynes and Their Applications in Synthesis of (E)-Enediynes

(E)-1-Iodo-2-arylselenoethylenes 1 underwent the Sonogashira coupling reactions with terminal alkynes 2 to afford (E)-1-arylseleno-substituted 1,3-enynes 3 in high yields. (E)-1-Arylseleno-substituted 1,3-enynes 3 were coupled with alkynylmagnesium bromides 4 in the presence of a catalytic amount of NiCl₂(PPh₃)₂ to give stereoselectively (E)-enediynes 5 in good yields.