Synthesis Of Allenes Research Articles

Allene Synthesis by Decomposition of Alkynyl N-Nosylhydrazones

Allene Synthesis by Decomposition of Alkynyl N-Nosylhydrazones

Synthesis of Allene Substituted Nipecotic Acids by Allenylation of Terminal Alkynes.

The relative reactivities of several secondary amines serving as hydride donors in propargylic amines undergoing a [1,5]-hydride transfer reaction to yield the respective terminal and 1,3-disubstituted allenes were studied. For this study, a two-step procedure was employed. At first, the synthesis of propargylic amines via the CuI-catalyzed aldehyde-alkyne-amine reactions (A3 coupling) was accomplished. The obtained propargylic amines were subsequently transformed to the desired allenes under CdI2 or ZnI2 catalysis. As a result, among the various secondary amines employed, differing in steric bulk, electronic nature, and conformational properties, allyl(tert-butyl)amine was found to be the best hydride donor for the synthesis of terminal allenes. For the synthesis of 1,3-disubstituted allenes, the propyne derivatives containing either a allyl(tert-butyl)amine or a 1,2,3,6-tetrahydropyridine unit in propargylic position performed best. Finally, with the developed procedure, nipecotic acid derivatives containing an N-allenyl substituent were synthesized with good yields using either ZnI2 as catalyst for the preparation of 1-substituted or CdI2 for the synthesis of 1,3-disubstitued allenes.

Dehydrative Cp*Co(III)-Catalyzed C-H Bond Allenylation.

An efficient, unprecedented reactivity of Cp*Co(III) for the synthesis of tetrasubstituted allenes under mild conditions is disclosed. Electron-rich and highly nucleophilic cobalt facilitates the dehydrative C-H bond allenylation directly from propargylic alcohols without any derivatization. The reaction proceeds via reversible cyclometalation followed by alcohol-directed regioselective alkyne insertion and β-hydroxy elimination to provide the tetrasubstituted allenes.

Highly Efficient Synthesis of Multi-Substituted Allenes from Propargyl­ Acetates and Organoaluminum Reagents Mediated by Palladium

A simple and mild catalytic SN2′ substitution reaction of propargyl acetates with organoaluminum reagents is reported. The SN2′ substitution reaction of propargyl acetates with organoaluminum reagents mediated by Pd(PhP3)2Cl2 (1 mol%)/PPh3 (2 mol%)/K2CO3 in tetrahydrofuran at 60 °C for 3–4 hours afforded the corresponding multi-substituted allenes in good yields (up to 94%) with high selectivities (up to 99%). The process was simple and easily performed, which offers an efficient method to synthesize the multi-substituted allene derivatives.

Copper‐Catalyzed Synthesis of Tetrasubstituted Allenes from Quaternary Ammonium Salts and Grignard Reagents

AbstractAlthough the synthesis of allenes has made considerable progress, methods for tetrasubstituted allenes are still limited. In this paper, the CuBr2‐catalyzed cross‐coupling reaction of Grignard reagents and propargylic ammonium salts in tetrahydrofuran at 60 °C under argon delivered tetrasubstituted allenes in good to excellent yields. The reaction is thought to proceed by an SN2′ pathway.

Enantioselective Synthesis of Allenes by Catalytic Traceless Petasis Reactions.

Allenes are useful functional groups in synthesis as a result of their inherent chemical properties and established reactivity patterns. One property of chemical bonding renders 1,3-substituted allenes chiral, making them attractive targets for asymmetric synthesis. While there are many enantioselective methods to synthesize chiral allenes from chiral starting materials, fewer methods exist to directly synthesize enantioenriched chiral allenes from achiral precursors. We report here an asymmetric boronate addition to sulfonyl hydrazones catalyzed by chiral biphenols to access enantioenriched allenes in a traceless Petasis reaction. The resulting Mannich product from nucleophilic addition eliminates sulfinic acid, yielding a propargylic diazene that performs an alkyne walk to afford the allene. Two enantioselective approaches have been developed; alkynyl boronates add to glycolaldehyde imine to afford allylic hydroxyl allenes, and allyl boronates add to alkynyl imines to form 1,3-alkenyl allenes. In both cases, the products are obtained in high yields and enantioselectivities.

Ti‐Catalyzed Synthesis of Exocyclic Allenes on Oxygen Heterocycles

A general method for the straightforward synthesis of exocyclic allenes on five‐, six‐, seven‐, and eight‐membered oxygen heterocycles is described. A Barbier‐type titanocene(III)‐catalyzed cyclization of propargyl halides with a pendant carbonyl group is the key step of the process. This reaction is compatible with many functional groups, and can be smoothly carried out under neutral and mild conditions at room temperature.

Synthesis of Multisubstituted Allenes, Furans, and Pyrroles via Tandem Palladium-Catalyzed Substitution and Cycloisomerization.

A palladium-catalyzed propargyl substitution reaction of propargyl acetates with indium organothiolates is developed for the synthesis of multisubstituted allenyl sulfides. This procedure can be applied to the synthesis of multisubstituted furans and pyrroles via tandem palladium-catalyzed propargyl substitution and cycloisomerization reaction in one pot.

Synthesis of Multisubstituted Allenes via Palladium-Catalyzed Cross-Coupling Reaction of Propargyl Acetates with an Organoaluminum Reagent

We describe a convenient method for the synthesis of multisubstituted allenes from cross-coupling of propargyl acetates with ­organoaluminum reagent: The reaction of propargyl acetates with 1.2 equivalents of organoaluminum reagent mediated by Pd(PPh₃)₂Cl₂ (1 mol%)/Ph₃P (2 mol%) and K₂CO₃ in THF may produce tri- or tetrasubstituted allenes in good to excellent yields (83–94%) and high regio­selectivities (up to 99%) at 60 °C in 3–4 hours.

Recent advances in catalytic asymmetric synthesis of allenes

This minireview summarizes the recent advances in the synthesis of allenes with catalytic asymmetric methods.

Pd/Cu cooperative catalysis: an efficient synthesis of (3-isoindazolyl)allenes via cross-coupling of 2-alkynyl azobenzenes and terminal alkynes.

An efficient synthesis of (3-isoindazolyl)allenes from 2-alkynyl azobenzenes and terminal alkynes via cooperative Pd(PPh3)2Cl2/CuI-catalyzed cross-coupling has been developed. By making use of this approach, (3-isoindazolyl)allenes with various substituents can be synthesized in good to excellent yields. A rapid synthesis of biologically active indazolo[2,3-a]quinoline was also achieved using this method as the key step.

Catalytic transient leaving group for atom-economic synthesis of allenes from 2-alkynols.

An atom economic approach from readily available propargylic alcohols to allenes, the first carboxylation of propargylic alcohols, has been established. Through the cooperative binary catalysis of Pd and a phosphoric acid, the reaction afforded multi-substituted allenoates with a broad scope tolerating useful functional groups. The synthetic potential of the obtained products has been demonstrated.

Enantioselective Synthesis of Trisubstituted Allenes via Cu(I)-Catalyzed Coupling of Diazoalkanes with Terminal Alkynes.

A highly enantioselective synthesis of trisubstituted allenes has been achieved through Cu(I)-catalyzed cross-coupling of aryldiazoalkanes and terminal alkynes with chiral bisoxazoline ligands. Alkynyl migratory insertion of Cu(I) carbene is proposed as the key step for the construction of axial chirality.

Synthesis of Allenes through Triazole Gold(III) Catalysed Rearrangement of Propargyl Vinyl Ethers

An efficient and simple method to the synthesis of allene derivatives was developed through pyridyltriazole gold(III) catalysed rearrangement of propargyl vinyl ethers with moderate to good yields. It was found that the pyridyltriazole gold(III) complex is a good chemoselective catalyst in selective activation of alkynes and allenes. Compared to gold(I) catalysts, the pyridyltriazole gold(III) shows much better substrate tolerance and much higher air and moisture stability.

Zn(OTf)2-Catalyzed Synthesis of Imidazole-Substituted Allenes.

A Zn(OTf)2-catalyzed simple and efficient method has been developed for the synthesis of imidazole-substituted allenes by the reaction of 1,1,3-triphenylprop-2-yn-1-ol and imidazoheterocycles. A library of tetrasubstituted allenes with broad functionalities have been prepared with excellent yields. The present methodology is also applicable to imidazo[1,2-a]pyrimidine, imidazo[2,1-b]thiazole and benzo[d]imidazo[2,1-b]thiazole.

ChemInform Abstract: Rh‐Catalyzed Stereospecific Synthesis of Allenes from Propargylic Benzoates and Arylboronic Acids.

AbstractThe first example of a rhodium catalyzed synthesis of optically active trisubstituted allenes from propargylic alcohol derivatives and arylboronic acid is presented.

ChemInform Abstract: Design and Synthesis of Alanine Triazole Ligands and Application in Promotion of Hydration, Allene Synthesis and Borrowing Hydrogen Reactions.

A new type of alanine triazole (ATA) ligand was found to be an efficient partner for the stabilization of gold(III), thus rendering improved stability and high catalytic activities in allene synthesis and hydration reactions through the 3,3′-arrangement of propargyl esters and propargyl alcohols. In addition to Au(I), ATA-gold(III) was also proven to be an effective catalyst in promoting the formation of allenes with high yields. Furthermore, alanine triazole ruthenium has exhibited excellent potential as a means to catalyze borrowing hydrogen of alcohols and amines, ketones and alcohols.

Stereoselective synthesis of exocyclic allenes by double hydride reduction of 3-alkynyl-2-cycloalkenones

Exocyclic allene natural products and pharmaceutical agents are rare but interesting compounds: Fucoxanthin, grasshopper ketone, and analogues of prostacyclins, cephalosporins, antithrombic agents and sterol biosynthesis inhibitors are representative. Syntheses of exocyclic allenes commonly rely on extended conjugate additions to e.g., alk-2-en-4-ynones, syn SN2′-like additions to alkynyl oxiranes, and substitution reactions such as electrophilic substitutions of propargylic silanes. We report that the reaction of 3-alkynyl-2-cycloalkenones with 2 equiv of various hydridoaluminates but not hydridoborates proceeds via diastereoselective 1,4-reduction of a vinylogously propargylic intermediate alcoholate to provide exocyclic allenes as major products. Isomeric 3-alkynylcycloalkanols also are observed.

Synthesis of Chiral Allenes by Rhodium(I) Catalysis

Key words rhodium catalysis - stereospecificity - allenes - phosphoramidite ligands

Design and Synthesis of Alanine Triazole Ligands and Application in Promotion of Hydration, Allene Synthesis and Borrowing Hydrogen Reactions

AbstractA new type of alanine triazole (ATA) ligand was found to be an efficient partner for the stabilization of gold(III), thus rendering improved stability and high catalytic activities in allene synthesis and hydration reactions through the 3,3′‐arrangement of propargyl esters and propargyl alcohols. In addition to Au(I), ATA‐gold(III) was also proven to be an effective catalyst in promoting the formation of allenes with high yields. Furthermore, alanine triazole ruthenium has exhibited excellent potential as a means to catalyze borrowing hydrogen of alcohols and amines, ketones and alcohols.magnified image