Cyclic Allenes Research Articles

ChemInform Abstract: Arene C—H Bond Functionalization Coupling with Cyclization of Allenes.

AbstractA rhodium(III)‐catalyzed reaction of N‐methoxybenzamides with tri‐ and tetrasubstituted 2,3‐allenols is developed to yield highly substituted 2,5‐dihydrofurans (III) and (VI).

ChemInform Abstract: Gorlos‐phos: Addressing the Stereoselectivity in Palladium‐Catalyzed exo‐Mode Cyclization of Allenes with a Nucleophilic Functionality.

AbstractA novel catalyst system is identified for addressing the long‐standing issue of Z/E stereoselectivity in Pd‐catalyzed exo‐mode cyclization reactions of allenes bearing nucleophilic functionality, such as (I), with organic halides or their equivalents.

Palladium(0)-Catalyzed Regioselective Synthesis of Macrocycles from Allenes with a Nucleophilic Functionality and Organic Iodides

A highly regioselective synthesis of 15–20-membered macrocycles via Pd(0)-catalyzed coupling cyclization of allenes bearing a carbon or nitrogen nucleophilic functionality and organic iodides is reported. After oxidative addition and carbopalladation, anti-π-allyl palladium intermediates were formed, which was followed by the exclusive intramolecular nucleophilic attack at the terminal carbon atom of the allene moiety to afford products with yields ranging from 44–92% and E/Z ratios of up to 97/3.

One‐Pot Zinc‐Promoted Asymmetric Alkynylation/Brook‐Type Rearrangement/Ene–Allene Cyclization: Highly Selective Formation of Three New Bonds and Two Stereocenters in Acyclic Systems

It's as easy as 1, 2, 3: In a one-pot sequence, two stereocenters and three new bonds were created with high selectivity through an asymmetric alkynylation of acyl silanes, a tandem Brook-type rearrangement and Zn-ene-allene cyclization, the addition of an electrophile, and finally oxidation. The straightforward nature of the synthetic procedure contrasts strongly with the complexity of the densely functionalized products obtained.

Regioselective Hydronickelation of Allenes and Its Application to the Hydrocyanative Carbocyclization Reaction of Allene–Ynes and Bis-Allenes

The carbocyanative cyclization of allene-ynes and bis-allenes under nickel catalysis is described. The key steps are the regioselective hydronickelation of allenes and subsequent cyclization via carbometalation. The former step determines the reaction pathway, and the latter controls the stereochemistry of substituted olefins. The products are useful carbo- and heterocycles that include a cyano group, functionalized double bonds, and quaternary carbons.

Synthesis of fused tetrahydropyrans by hydroalkoxylation of δ-hydroxy allenes

Fused tetrahydropyrans were synthesized by silver(I)- and mercury(II)-mediated intramolecular hydroalkoxylations of δ-hydroxy allenes installed on a tetrahydropyran template. Cyclization of simple allenes was promoted by silver perchlorate to afford vinyl-substituted trans-fused bis-tetrahydropyrans, whereas cyclization of methyl-substituted allenes at the internal allenic carbon atom was achieved more effectively with a catalytic amount of mercuric triflate rather than with silver salts.

Arene CH Bond Functionalization Coupling with Cyclization of Allenes

AbstractUnder the catalysis of a rhodium(III) complex, the cyclization of 2,3‐allenols was most probably initiated with the CH bond functionalization of N‐methoxybenzamides using the tetramethylcyclopentadiene anion (C5Me4−) as ligand, affording differently substituted 2,5‐dihydrofuran derivatives. Highly efficient axial‐to‐central chirality transfer has been observed.

Synthesis of seven-membered cyclic allenes, 1-zirconacyclohepta-2,3,6-trienes, from alkynes and 1-en-3-ynes

Seven-membered metallacyclic allene compounds, 1-zirconacyclohepta-2,3,6-trienes, were synthesized by intermolecular coupling between alkynes and 1-en-3-ynes on a zirconium atom. X-ray diffraction studies and NMR spectroscopic observation indicated their seven-membered structures, although the contribution from 2-alkynyl-1-zirconacyclopent-4-ene might be considered. Benzyne, an unstable alkyne, also coupled with 1-en-3-ynes on zirconium and titanium.

Dual Catalysis: A Chiral Amine and Palladium Mediated Allene Cyclization

Dual Catalysis: A Chiral Amine and Palladium Mediated Allene Cyclization

Gorlos-phos: addressing the stereoselectivity in palladium-catalyzed exo-mode cyclization of allenes with a nucleophilic functionality

A novel catalyst system has been indentified for addressing the long-standing issue of Z/E stereoselectivity in palladium-catalyzed exo-mode cyclization reactions of allenes bearing a nucleophilic functionality with organic halides or their equivalents. The readily accessible, sterically hindered monophosphine ligand Gorlos-Phos·HBF4 imparts a remarkable stereocontrolling ability with broad generality under Pd catalysis.

ChemInform Abstract: Carcerands and Hemicarcerands

AbstractReview: 189 refs.

“Total Synthesis of Bioactive Natural Products by Palladium-Catalyzed Domino Cyclization of Allenes and Related Compounds”

Chemistry Research Laboratory, University of Oxford, 12 Mansfi eld Road, Oxford OX1 3TA, UK Email: edward.anderson@chem.ox.ac.uk In the latest contribution to the “Springer Theses” series, which celebrate outstanding graduate research from the physical sciences, Shinsuke Inuki provides a detailed account of his PhD research, entitled “Total Synthesis of Bioactive Natural Products by Palladium-Catalyzed Domino Cyclization of Allenes and Related Compounds”. Inuki carried out this work in the laboratory of Professor Hiroaki Ohno (Kyoto University, Japan), whose young research group has established a reputation in the fi eld of late transition metal-catalysed ‘cascade’ organic reactions (also known as ‘domino’ reactions) involving alkynes and allenes. The target audience for the book includes practicing organic chemists with interests in synthesis, and those with specifi c interests in palladium-catalysed organic reactions, and as such is suited to graduate level and above. As the title suggests, the book delves extensively into mechanistic aspects of palladium-catalysed allene chemistry, with a focus on two reaction types: intramolecular reactions of allenylpalladium(II) complexes with pendant nucleophiles, and intramolecular reactions of allenes activated by pendant palladium(II) species (Scheme I). The key feature of these processes is the ability of the palladium(II) catalyst to enhance the electrophilicity of the allene through coordination to the metal atom in its +2 oxidation state, thus triggering nucleophilic attack. Having established an understanding of each metal-catalysed bicyclisation, Inuki goes on to apply this chemistry to the synthesis of a number of bioactive alkaloid natural products. The overall aims of the work are fi rstly to extend the state of the art in palladium-activated allene chemistry through a “Total Synthesis of Bioactive Natural Products by Palladium-Catalyzed Domino Cyclization of Allenes and Related Compounds”

Allenylphosphonates/Allenylphosphine Oxides as Intermediates/Precursors for Intramolecular Cyclization Leading to Phosphorus-Based Indenes, Indenones, Benzofurans, and Isochromenes

Utilizing internally available functional groups, a simple protocol for the efficient synthesis of phosphorus-based indenes, indenones, benzofurans, and isochromenes via intramolecular cyclization of allene intermediates/precursors is generated; the latter intermediates/precursors are conveniently obtained through aldehyde-, alkylidene-, and hydroxyl-functionalized propargyl alcohols and P(III)-Cl precursors. The structures of key products have been unequivocally confirmed by X-ray crystallography.

Ruthenium‐Catalyzed Intramolecular [2+2+2] Cyclization of Allene–Yne–Enes: Construction of Fused‐Tricyclic Skeletons

Three's not a crowd: An intramolecular [2+2+2] cyclization between three different components, allene, alkyne, and alkene, has been realized using a catalytic amount of [Cp*RuCl(cod)] complex (cod = 1,5-cyclooctadiene), and afforded fused-tricyclic compounds in a highly stereoselective manner.

Chemistry of the five-membered zirconacycloallenoids: reactions with unsaturated substrates

Zirconocene, in situ generated by treatment of zirconocene dichloride with two molar equiv. of n-butyl magnesium chloride, is trapped by the enynes R–CC–C(Me)CH2 (R = –SiMe3, 7c; R = tert-butyl, 7b) to give the zirconacycloallenoids 6b and 6c, respectively. Compound 6c adds an additional equivalent of the enyne 7c to form the seven-membered alkyne insertion product 9 which itself exhibits a typical zirconacycloallenoid structure. Acetonitrile insertion into the Zr–C bond of 6c also results in the formation of a seven-membered metallacycloallenoid, isolated as the respective enamido tautomer 10. Compound 6c reacts with two molar equiv. of benzaldehyde to give a nine-membered cyclic allene. Compound 6b adds one molar equiv. of the enyne 7c to yield the nine-membered metallacycle 14 that contains two metal bonded allenoid moieties inside the ring structure.

Concerted vs Stepwise Mechanisms in Dehydro-Diels–Alder Reactions

The Diels-Alder reaction is not limited to 1,3-dienes. Many cycloadditions of enynes and a smaller number of examples with 1,3-diynes have been reported. These "dehydro"-Diels-Alder cycloadditions are one class of dehydropericyclic reactions which have long been used to generate strained cyclic allenes and other novel structures. CCSD(T)//M05-2X computational results are reported for the cycloadditions of vinylacetylene and butadiyne with ethylene and acetylene. Both concerted and stepwise diradical routes have been explored for each reaction, with location of relevant stationary points. Relative to 1,3-dienes, replacement of one double bond by a triple bond adds 6-6.5 kcal/mol to the activation barrier; a second triple bond adds 4.3-4.5 kcal/mol to the barrier. Product strain decreases the predicted exothermicity. In every case, a concerted reaction is favored energetically. The difference between concerted and stepwise reactions is 5.2-6.6 kcal/mol for enynes but diminishes to 0.5-2 kcal/mol for diynes. Experimental studies on intramolecular diyne + ene cycloadditions show two distinct reaction pathways, providing evidence for competing concerted and stepwise mechanisms. Diyne + yne cycloadditions connect with arynes and ethynyl-1,3-cyclobutadiene. This potential energy surface appears to be flat, with only a minute advantage for a concerted process; many diyne cycloadditions or aryne cycloreversions will proceed by a stepwise mechanism.

ChemInform Abstract: Stereoselective Synthesis of Pyrrolo[1,2‐a]indoles from Allenes in PEG‐400 as the Reaction Medium.

AbstractBase‐catalyzed domino cyclization of allenes with 2‐formylindoles affords the targets as single products.

A [4+4] annulation strategy for the synthesis of eight-membered carbocycles based on intramolecular cycloadditions of conjugated enynes

A [4+4] annulation strategy for the synthesis of eight-membered carbocycles is reported that proceeds via a cascade involving two pericyclic processes. In the first step, the [4+2] cycloaddition of a conjugated enyne with an electron-deficient cyclobutene generates a strained six-membered cyclic allene that isomerizes to the corresponding 1,3-cyclohexadiene. In the second step, this bicyclo[4.2.0]octa-2,4-diene intermediate undergoes thermal or acid-promoted 6-electron electrocyclic ring opening to furnish a 2,4,6-cyclooctatrienone. The latter transformation represents the first example of the promotion of 6-electron electrocyclic ring opening reactions by acid.

ChemInform Abstract: A Synthesis of 2‐epi‐Fagomine Using Gold(I)‐Catalyzed Allene Cyclization.

AbstractA highly stereoselective Au(I)‐catalyzed cyclization of allene (IV) is the key step in the synthesis of 2‐epi‐fagomine (VI).

First Synthesis of Medium‐Sized Ring Allenyl Lactams

AbstractMedium‐sized lactams bearing an axially chiral allene unit have been synthesized by using an aza‐ketene Claisen rearrangement. Starting from 2‐alkynylpiperidines or 2‐alkynylazepines, ring enlargement enabled the highly diastereoselective formation of 10‐ or 11‐membered lactams with a 4,5‐allene subunit. X‐ray analysis of the allenylacezinone showed the presence of a strained cumulated olefin system with a defined arrangement of the functional groups. The cyclic allenes were found to be stable upon heating up to 50 °C.