Allenamides: a powerful and versatile building block in organic synthesis

Palladium-catalyzed cascade metallo-ene/Suzuki coupling reaction of allenamides

A new type of cascade metallo-ene/Suzuki coupling reaction of allenamides catalyzed by palladium is described.

Transfer of axial chirality through the nickel-catalysed hydrocyanation of chiral allenes

The transfer of axial chirality of allenes is beginning to be exploited as a powerful method for creating central chirality, particularly through the use of transition metal catalysis.

Synthesis of 6-methyl-3,4-dihydropyrazinones using an Ugi 4-CR/allenamide cycloisomerization protocol

A two-step synthesis of 6-methyl-3,4-dihydropyrazinones from Ugi adducts and their transformation into pyrazino[2,1-a]isoindole and pyrazino[2,1-a]isoquinoline cores has been accomplished.

TBAF catalyzed one-pot synthesis of allenyl-indoles

The site selective synthesis of functionalized indoles is presented under environmentally convenient tetrabutylammonium fluoride catalysis.

Rhodium-Catalyzed Regio- and Stereoselective [2 + 2] Cycloaddition of Allenamides

A highly regio- and stereoselective Rh-catalyzed intermolecular head-to-head [2 + 2] cycloaddition of allenamides was developed. The intermolecular cycloadducts, trans-dimethylenecyclobutane-1,2-diamine derivatives, were achieved in good yields with high regioselectivity and stereoselectivity.

New opportunities in the stereoselective dearomatization of indoles

The regio- and stereoselective dearomatization of indoles is realized for the first time by combining readily available indolyl precursors and electron-rich allenes, namely allenamides and aryloxyallenes. Inter- as well as intramolecular condensations were realized under gold and Brønsted acid catalysis providing a range of densely functionalized indoline and indolenine cores in high yields and excellent stereochemical outcome. Chemodivergent reaction profiles (Micheal-type addition vs. [2+2]-cycloaddition) were realized by a tailored design of both reaction conditions and functionalization of the reaction partners.

Asymmetric addition of α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid

Asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid catalyst, generates an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity.

We describe the asymmetric addition of unactivated α-branched cyclic ketones to allenamides catalyzed by a chiral phosphoric acid, generating an all-carbon quaternary stereocenter with broad substrate scope and high enantioselectivity. The products are easily transformed into their corresponding 1,5- and 1,4-ketoaldehyde derivatives, which are both important building blocks in organic synthesis.

Base-promoted intramolecular cyclization of N-alkyl, N-propargylic β-enaminones for the synthesis of polysubstituted pyrroles

An efficient, mild, metal-free, base-mediated intramolecular cyclization of N-alkyl, N-propargylic β-enaminones has been realized for the generation of polysubstituted pyrrole derivatives.

Gold(i) operational in synergistic catalysis for the intermolecular α-addition reaction of aldehydes across allenamides

A synergistic approach to the catalytic intermolecular α-addition of aldehydes across allenamides using gold(i) and proline derivatives.

Suzuki coupling for preparation of allenes – ligand effects and chirality transfer

o-(Diphenylphosphino)benzaldehyde has been identified as the effective ligand for the coupling of propargylic carbonates and organoboronic acids under mild conditions.

Synergistic gold and enamine catalysis: intermolecular α-alkylation of aldehydes with allenamides

Aldehydes can be α-alkylated with allenamides by the combined action of an organocatalyst and a gold complex.

Gold-catalyzed [3+2]-annulations of α-aryl diazonitriles with ynamides and allenamides to yield 1-amino-1H-indenes

Gold-catalyzed [3+2]-annulations of α-aryl diazonitriles with ynamides and allenamides yielding 1-amino-1H-indenes in two distinct pathways have been reported.

Enantioselective gold-catalyzed intermolecular [2 + 2]-cycloadditions of 3-styrylindoles with N-allenyl oxazolidinone

A series of novel chiral monophosphine ligands Xiang-Phoses were designed and have been applied to the enantioselective gold-catalyzed intermolecular [2 + 2]-cycloaddition of 3-styrylindoles 1 with N-allenyl oxazolidinone 2.

Why base-catalyzed isomerization of N-propargyl amides yields mostly allenamides rather than ynamides

The base-catalyzed isomerization of N-propargylamides or carbamates may furnish N-allenyl compounds (allenamides/allencarbamates) or further evolve to N-alkynyl compounds (ynamides or yncarbamates). The particular fate of this reaction varies from experiment to experiment and there is no clear rule for predicting the reaction outcome for a particular structure. With the support of ab initio and DFT computations, this work shows that observed results can be explained by assuming an exchange equilibrium between energetically close N-propargyl, allenyl and N-alkynyl forms and that the reaction outcome correlates to a particular equilibrium mixture. Due to the very small energy gap between the N-allenyl and N-alkynyl forms, small structural changes may easily alter the equilibrium position, explaining the variety of observed experimental results. Based on CBS-QB3 computations, the ωB97 functional provided reasonably accurate isomerization energies and could successfully predict the experimentally observed behavior for several examples from the literature.

Enantioselective gold catalyzed dearomative [2+2]-cycloaddition between indoles and allenamides

The highly enantioselective synthesis of densely functionalized 2,3-indoline-cyclobutanes by means of chiral gold catalysis is presented. Intermolecular formal [2+2]-cycloaddition reactions between substituted indoles and allenamides enabled direct access to methylenecyclobutane-fused indolines, featuring two consecutive quaternary stereogenic centers with excellent stereochemical control (dr > 20 : 1, ee up to 99%).

Base-Promoted N-Pyridylation of Heteroarenes Using N-Propargyl Enaminones as Equivalents of Pyridine Scaffolds

N-Pyridylation of various N-heteroarenes, including N-heteroarene-containing peptides, was achieved using N-propargyl enaminones (isolated or generated in situ from propargyl amine and propynones) as masked polysubstituted pyridine cores. This metal-free procedure proceeds under mild reaction conditions and generates 1 equiv of H2O as the sole byproduct.

Enantioselective gold-catalyzed intermolecular [2+2] versus [4+2]-cycloadditions of 3-styrylindoles with N-allenamides: observation of interesting substituent effects

The cycloaddition mode ([2+2] vs. [4+2]) can be unexpectedly switched by the simple modification of the N-substituent of the 3-styrylindoles.

A highly enantioselective [2+2] versus a [4+2]-cycloaddition of 3-styrylindoles to N-allenamides catalyzed by identical gold(i)/chiral phosphoramidite complexes is presented, which provides facile access to synthetically valuable, optically active substituted cyclobutanes and tetrahydrocarbazoles. The cycloaddition mode unexpectedly depends on the electronic nature of the N-substituent 3-styrylindoles, the origin of which could be well rationalized using DFT calculations and experimental results. To the best of our knowledge, the present work represents the first example of such an impressive substituent effect in tuning the reaction mode with high chemo-, regio- and enantioselectivity in asymmetric gold catalysis.

Gold(i)-catalyzed [2 + 2 + 2] cycloaddition of allenamides, alkenes and aldehydes: a straightforward approach to tetrahydropyrans

Allenamides participate as two-carbon components in an intermolecular [2 + 2 + 2] cycloaddition with alkenes and aldehydes when treated with catalytic amounts of a phosphite gold complex. The reaction is highly regio- and chemoselective, and works with different types of alkenes, including styrenes, enol ethers or enamides, as well as with aromatic and aliphatic aldehydes. Accordingly, different types of 2,6-disubstituted tetrahydropyrans can be stereoselectively assembled in a single step from commercial or very accessible starting materials.

Regioselective Synthesis of Highly Substituted Imidazoles via the Sequential Reaction of Allenyl Sulfonamides and Amines

A novel synthesis of imidazoles from electron-withdrawing group-substituted allenyl sulfonamides with amines was developed. The 4- and 5-functionalized imidazoles were constructed regioselectively, which depended on the substituents on the nitrogen atoms.

Ruthenium-catalyzed C-C coupling of fluorinated alcohols with allenes: dehydrogenation at the energetic limit of β-hydride elimination

Ruthenium(II) complexes catalyze the CC coupling of 1,1-disubstituted allenes and fluorinated alcohols to form homoallylic alcohols bearing all-carbon quaternary centers with good to complete levels of diastereoselectivity. Whereas fluorinated alcohols are relatively abundant and tractable, the corresponding aldehydes are often not commercially available because of their instability.