Functionalization Of Allenes Research Articles

Visible-Light-Mediated Dual Functionalization of Allenes: Regio- and Stereoselective Synthesis of Vinylsulfone Azides.

A gentle and effective method for the photocatalytic dual functionalization of allenes with high regio- and stereoselectivity using a nonmetallic catalyst is described. Inexpensive and easily available sulfinates and TMSN3 were employed as sulfone and azido sources, respectively. The method is characterized by satisfactory substrate compatibility and tolerance toward functional groups. The straightforward initial mechanistic experiments suggested that the reaction could follow a radical pathway. The synthesis of vinylsulfone azide derivatives presented here offers a promising scaffold for the future development of vinyl sulfone-based drugs and functional bioorthogonal reagents.

Photochemical Metal‐Hydride Hydrogen Atom Transfer Mediated Radical Hydrofunctionalization of Dienes and Allenes

AbstractThe metal‐hydride hydrogen atom transfer (MHAT) method is widely recognized as a powerful technique for functionalizing alkenes. However, its application in the functionalization of industrial feedstock dienes and allenes is relatively rare due to challenges related to chemo‐selectivity. In recent studies, Co‐porphines have been identified as highly efficient catalysts under photoirradiation for MHAT, demonstrating an exceptional level of chemoselectivity for the functionalization of dienes and allenes, while disregarding other simple olefins present. This novel method enables the selective reductive coupling of pyridines with dienes and the allylation of aldehydes by the combination with Ti catalysis. Mechanistic studies and density functional theory (DFT) calculations support the idea that the non‐reversible transfer of hydrogen atoms from cobalt hydride to dienes and allenes, leading to the generation of allyl radicals, is the key step in the catalytic cycle.

Synthesis of 1,1-Disubstituted Allenylic Silyl Ethers Through Iron-Catalyzed Regioselective C(sp2)─H Functionalization of Allenes.

We report a synthesis of allenylic silyl ethers through iron-catalyzed functionalization of the C(sp2)─H bonds of monosubstituted alkylallenes. In the presence of a cyclopentadienyliron dicarbonyl based catalyst and triisopropylsilyl triflate as a silylation agent, a variety of aryl aldehydes were suitable coupling partners in this transformation, furnishing a collection of 1,1-disubstituted allenylic triisopropylsilyl ethers as products in moderate to excellent yields as a single regioisomer. Lithium bistriflimide was identified as a critical additive in this transformation. The optimized protocol was scalable, and the products were amenable to further transformation to give a number of unsaturated, polyfunctional derivatives.

Asymmetric Organocatalytic Reactions of Activated Racemic Allenes

AbstractAsymmetric organocatalytic reactions of various electron‐deficient racemic allenes with a wide variety of nucleophiles and electrophiles were reviewed. The literature on enantioselective functionalization of allenes that employs chiral phosphine, amine, phase transfer, bifunctional, and Brønsted acid catalysis is presented along with the mechanisms. In addition, the review emphasizes methods of obtaining enantioenriched allenes from racemic allenes via organocatalytic (dynamic) kinetic resolution techniques. The synthetic utility of the developed methodologies toward the target‐orientated biologically active molecules is narrated along with the examples.

Copper-Catalyzed Diastereo- and Enantioselective Borylative Cyclization

Copper-catalyzed enantioselective borylative cyclization with various electrophiles via difunctionalization of unsaturated hydrocarbons is a powerful tool for the generation of interesting boron-containing carbocycles and heterocycles processes involving a chiral organocopper intermediate. Alkenes, allenes, and alkynes are versatile and easily accessible substrates that can be subjected to a wide range of reactions to produce densely functionalized, enantioenriched products. In this chapter, I discuss copper-catalyzed alkenes, allenes, and alkynes borofunctionalization and enantioselective cyclization via chiral organocopper intermediate. Copper-catalyzed enantioselective borylative cyclization and regiodivergent functionalization of alkenes, allenes, and alkynes, as well as the current mechanistic understanding of such processes, are given special attention in this review.

Correction: Electrochemically-mediated C–H functionalization of allenes and 1,3-dicarbonyl compounds to construct tetrasubstituted furans

Correction for ‘Electrochemically-mediated C–H functionalization of allenes and 1,3-dicarbonyl compounds to construct tetrasubstituted furans’ by Mu-Xue He et al., Org. Chem. Front., 2022, DOI: 10.1039/d1qo01458g.

Electrochemically-mediated C–H functionalization of allenes and 1,3-dicarbonyl compounds to construct tetrasubstituted furans

We reported an electrocatalytic C–H activation method to construct novel highly functionalized tetrasubstituted furan derivatives, which uses allenes and 1,3-dicarbonyl compounds as substrates.

Deciphering the Chameleonic Chemistry of Allenols: Breaking the Taboo of a Onetime Esoteric Functionality.

The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products.

Visible light mediated functionalization of allenes

This review summarizes the visible light mediated strategies for the functionalization of allenes.

Synthesis and Functionalization of Allenes by Direct Pd‐Catalyzed Organolithium Cross‐Coupling

AbstractA palladium‐catalyzed cross‐coupling between in situ generated allenyl/propargyl‐lithium species and aryl bromides to yield highly functionalized allenes is reported. The direct and selective formation of allenic products preventing the corresponding isomeric propargylic product is accomplished by the choice of SPhos or XPhos based Pd catalysts. The methodology avoids the prior transmetalation to other transition metals or reverse approaches that required prefunctionalization of substrates with leaving groups, resulting in a fast and efficient approach for the synthesis of tri‐ and tetrasubstituted allenes. Experimental and theoretical studies on the mechanism show catalyst control of selectivity in this allene formation.

Synthesis and Functionalization of Allenes by Direct Pd-Catalyzed Organolithium Cross-Coupling.

A palladium-catalyzed cross-coupling between in situ generated allenyl/propargyl-lithium species and aryl bromides to yield highly functionalized allenes is reported. The direct and selective formation of allenic products preventing the corresponding isomeric propargylic product is accomplished by the choice of SPhos or XPhos based Pd catalysts. The methodology avoids the prior transmetalation to other transition metals or reverse approaches that required prefunctionalization of substrates with leaving groups, resulting in a fast and efficient approach for the synthesis of tri- and tetrasubstituted allenes. Experimental and theoretical studies on the mechanism show catalyst control of selectivity in this allene formation.

Nickel Catalyzed Functionalization of Allenes

AbstractOver the past few years, nickel catalysis “encountered” allenes in organic transformations, opening direct access to a plethora of chemical scaffolds in straightforward manner. The activation of allenes or their reaction partners by means of [Ni(0)] as well as [Ni(II)] species enabled chemical diversity and complexity to be achieved simultaneously through desirable concepts like selectivity, functional group tolerance and mildness. An overview of the most recent findings in the area is presented herein.

Reprint of: Recent advances in the functionalization of allenes via radical process

This review is focused on the recent advances in the functionalization of allenes via radical process. Different radical partners including carbon radicals and heteroatom radicals are discussed in the reactions of allenes. Generally, the radical formed in situ would attack the allene at the central carbon leading to allyl radical intermediate. However, the formation of alkenyl radical intermediate from allene could be observed as well in some cases with high regioselectivity and stereoselectivity.

Recent advances in the functionalization of allenes via radical process

This review is focused on the recent advances in the functionalization of allenes via radical process. Different radical partners including carbon radicals and heteroatom radicals are discussed in the reactions of allenes. Generally, the radical formed in situ would attack the allene at the central carbon leading to allyl radical intermediate. However, the formation of alkenyl radical intermediate from allene could be observed as well in some cases with high regioselectivity and stereoselectivity.

Creation of Novel Cyclization Methods Using sp-Hybridized Carbon Units and Syntheses of Bioactive Compounds.

Some recent results on the development of new and reliable procedures for the construction of diverse ring systems based on the chemistry of sp-hybridized species, especially allene functionality, are described. This review includes: (i) synthesis of the multi-cyclic skeletons by combination of the π-component of allene with suitable other π-components such as alkyne, alkene, or additional allene under Rh-catalyzed conditions; (ii) synthesis of heterocycles as well as carbocycles by reaction of the sp-hybridized center of allene with some nucleophiles in an endo-mode manner; and (iii) total syntheses of natural products and related compounds from the sp-hybridized starting materials.

Stereoselective Synthesis of Chiral Polycyclic Indolic Architectures through Pd(0) -Catalyzed Tandem Deprotection/Cyclization of Tetrahydro-β-carbolines on Allenes.

Enantioenriched N-allyl tetrahydro-β-carbolines were prepared by chiral phosphoric acid-catalyzed Pictet-Spengler reactions. The compounds undergo Pd(0) -catalyzed cyclizations through a tandem deprotection/cyclization process. The regioselectivity of the attack is controlled by the chain length and by the substitution pattern of the allene function. Products resulting from 5-exo- or 6-exo-attack were obtained with diastereoisomeric ratio up to 95:5. Azepinopyrrido[3,4-b]indoles were obtained by 7-endo-cyclizations.

Mechanisms of syn-insertion of alkynes and allenes into gold-silicon bonds: a comprehensive experimental/theoretical study.

A detailed mechanistic study is reported for the syn-insertion of alkynes and allenes in the Au-Si bonds of complexes (R3P)Au-SiR'Ph2 (R = Ph, Me and R' = t-Bu, Ph). Kinetic experiments indicate that (i) the reaction is first-order in alkyne and gold silyl complex and (ii) it requires a rather low enthalpy of activation and a relatively large negative entropy of activation [ΔH(‡) = 13.7 (±1.6) kcal·mol(-1) and ΔS(‡) = -32.0 (±5.0) cal·mol(-1)·K(-1) for the reaction of (Ph3P)Au-Si(t-Bu)Ph2 with methyl propiolate], in line with a bimolecular associative transformation. The different mechanistic pathways have been explored by DFT calculations. Accordingly, the reaction is found to proceed via a two-step inner-sphere mechanism: (i) first, the alkyne coordinates to the gold silyl complex to form a π-complex; (ii) the subsequent migratory insertion step is rate determining and occurs in a concerted manner. Provided dispersion effects are taken into account (B97D functional), the enthalpy of activation estimated theoretically [ΔH(‡) = 11.5 kcal·mol(-1)] is in good agreement with that measured experimentally. The influence of the π substrate (methyl propiolate, dimethyl acetylene dicarboxylate, phenyl acetylene, ethyl 2,3-butadienoate) has been analyzed theoretically, and the regioselectivity of the insertion has been rationalized. In particular, the unexpected selectivity observed experimentally with the allene is shown to result from the insertion of the terminal nonactivated C═C double bond into the Au-Si bond of (Ph3P)Au-SiPh3, followed by an original isomerization (Au/Si exchange process). This study provides unambiguous evidence for coordination-insertion at gold and thereby strongly supports the possible occurrence of inner-sphere mechanisms during the functionalization of alkynes and allenes.

ChemInform Abstract: [2 + 2 + 1] Cyclization of Allenes

AbstractReview: 94 refs.

Pd(0)-Catalyzed Tandem Deprotection/Cyclization of Tetrahydro-β-carbolines on Allenes: Application to the Synthesis of Indolo[2,3-a]quinolizidines

The pallado-catalyzed tandem deprotection/cyclization reaction of enantioenriched N-allyl tetrahydro-β-carbolines on allenes is described. The first step generates in situ a deprotected tetrahydro-β-carboline, which then undergoes a cyclization on the allene function via an intermediate π-allyl Pd(II) derivative. This reaction results in the synthesis of various chiral indolic tetracycles (mainly indolo[2,3a]quinolizidine derivatives) presenting a vinyl function.

2+2+1] Cyclization of allenes

The [2+2+1] cyclization of an alkyne, an alkene and carbon monoxide, i.e., the Pauson-Khand reaction, is one of the most powerful tools for constructing a five-membered ring. In place of the alkene or alkyne part, the use of an allene functionality has proven to make this reaction more valuable for organic synthesis. This review focuses on the origin and progress of the allenic [2+2+1] cyclocarbonylation, including the chirality transfer of the allene and its synthetic applications.