Allyl Migration Research Articles

Directing the Stereoselectivity of the Claisen Rearrangement to Form Cyclic Ketones with Full Substitution at the α-Positions.

We report an enantioselective synthesis of cyclic ketones with full substitutions at the α-positions in a highly diastereoselective manner. Our method is achieved by subjecting substrate motifs in 2-allyloxyenones to chiral organomagnesium reagents, which trigger the Claisen rearrangement upon direct 1,2-carbonyl addition. The observed diastereoselectivity of the allyl migration is proposed to originate from the intramolecular chelation of the magnesium alkoxide to the allyloxy moiety.

Conversion of 5-methyl-4H-benzo[d][1,3]dioxin-4-one derivatives into functionalized 8-hydroxyisochroman-1-one under basic conditions

Syntheses of 8-hydroxyisochroman-1-one derivatives are described, promoted via a base-induced anionic accelerated rearrangement reaction from dimethyl dioxinone protected resorcylates. A biomimetic polyketide aromatization strategy via selective C-acylation of a β-keto ester, Pd(0)-catalyzed allylic migration and base-promoted cyclization and aromatization furnished the arene core of the resorcylate precursors.

Ruthenium(II)-Catalyzed Migratory C–H Allylation/Hydroamination Cascade for the Synthesis of Rutaecarpine Analogues

An unprecedented allyl migration from a remote position of a quinazoline moiety through a ruthenium(II) shuttle is reported. This present cascade reaction is initiated through the formation of an η3-ruthenium–allyl complex followed by C–H allylation at the ortho position of the 2-aryl moiety. Finally, hydroamination with the quinazolinone -NH group, which is formed through tautomerization of the quinazoline, furnishes the annulation product. This exceedingly fast cascade reaction is complete within 10 minutes to provide rutaecarpine analogues in a single operation.

The Synthesis of (±)‐Oxyisocyclointegrin

The total synthesis of oxyisocyclointegrin is described. The key steps in the synthesis included a Tsuji–Trost allyl migration to exclusively afford the corresponding monoallylated 1,3‐diketone and a photochemical initiated oxidative cyclization to forge the oxepine core.

Synthesis of benzothiophene and indole derivatives through metal-free propargyl-allene rearrangement and allyl migration.

An efficient base-catalyzed protocol for the synthesis of benzothiophene is described. The reaction proceeds via base-promoted propargyl–allenyl rearrangement followed by cyclization and allyl migration. Phosphine-substituted indoles can be synthesized by a similar strategy.

Gold(I)‐Catalyzed Carboaminations of Allenes by N‐Allyltetrahydro‐β‐carbolines: An Experimental and Theoretical Study

AbstractN‐Allyltetrahydro‐β‐carbolines bearing a pendant allene undergo unprecedented gold(I)‐catalyzed cyclizations proceeding with an allyl migration from the nitrogen to the allene moiety. The initial product of the gold‐catalyzed cyclization evolves either via isomerization or Cope rearrangement, leading to different scaffolds. Density function theory (DFT) calculations established that the allyl migration occurs in an asynchronous suprafacial manner.magnified image

ChemInform Abstract: Sequential Ketene Generation from Dioxane‐4,6‐dione‐keto‐dioxinones for the Synthesis of Terpenoid Resorcylates.

AbstractKiegiel‐type reaction of alcohols with the ketene generated in situ by thermolysis of compound (I) furnishes dioxinone‐β‐ketoesters which are transformed into the title compounds by Pd(0)‐catalyzed decarboxylative allyl migration and aromatization.

Modular, Catalytic Enantioselective Construction of Quaternary Carbon Stereocenters by Sequential Cross-Coupling Reactions.

The catalytic Suzuki-Miyaura cross-coupling with chiral γ,γ-disubstituted allylboronates in the presence of RuPhos ligand occurs with high regioselectivity and enantiospecificity, furnishing nonracemic compounds with quaternary centers. Mechanistic experiments suggest that the reaction occurs by transmetalation with allyl migration, followed by rapid reductive elimination.

Sequential Ketene Generation from Dioxane-4,6-dione-keto-dioxinones for the Synthesis of Terpenoid Resorcylates.

Trapping of the ketene generated from the thermolysis of 2-methyl-2-phenyl-1,3-dioxane-4,6-dione-keto-dioxinone at 50 °C with primary, secondary, or tertiary alcohols gave the corresponding dioxinone β-keto-esters in good yield under neutral conditions. These intermediates were converted by palladium(0)-catalyzed decarboxylative allyl migration and aromatization into the corresponding β-resorcylates. These transformations were applied to the syntheses of the natural products (±)-cannabiorcichromenic and (±)-daurichromenic acid.

ChemInform Abstract: Enantioselective Synthesis of Pyrrole‐Based Spiro‐ and Polycyclic Derivatives by Iridium‐Catalyzed Asymmetric Allylic Dearomatization and Controllable Migration Reactions.

The first highly diastereo- and enantioselective synthesis of five-membered spiro-2H-pyrroles was achieved using an Ir-catalyzed asymmetric allylic dearomatization reaction. The spiro-2H-pyrrole derivatives readily undergo a controllable and stereospecific allylic migration under acid catalysis, providing polycyclic pyrrole derivatives in excellent yields and ee values. Additionally, the novel Ir-complex K1, derived from [Ir(cod)Cl]2 (cod=1,5-cyclooctadiene) and N-benzhydryl-N-phenyldinaphthophosphoramidite (BHPphos), showed excellent control of both diastereo- and enantioselectivities.

Enantioselective Synthesis of Pyrrole-Based Spiro- and Polycyclic Derivatives by Iridium-Catalyzed Asymmetric Allylic Dearomatization and Controllable Migration Reactions.

The first highly diastereo- and enantioselective synthesis of five-membered spiro-2H-pyrroles was achieved using an Ir-catalyzed asymmetric allylic dearomatization reaction. The spiro-2H-pyrrole derivatives readily undergo a controllable and stereospecific allylic migration under acid catalysis, providing polycyclic pyrrole derivatives in excellent yields and ee values. Additionally, the novel Ir-complex K1, derived from [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) and N-benzhydryl-N-phenyldinaphthophosphoramidite (BHPphos), showed excellent control of both diastereo- and enantioselectivities.

Enantioselective Synthesis of Pyrrole‐Based Spiro‐ and Polycyclic Derivatives by Iridium‐Catalyzed Asymmetric Allylic Dearomatization and Controllable Migration Reactions

AbstractThe first highly diastereo‐ and enantioselective synthesis of five‐membered spiro‐2H‐pyrroles was achieved using an Ir‐catalyzed asymmetric allylic dearomatization reaction. The spiro‐2H‐pyrrole derivatives readily undergo a controllable and stereospecific allylic migration under acid catalysis, providing polycyclic pyrrole derivatives in excellent yields and ee values. Additionally, the novel Ir‐complex K1, derived from [Ir(cod)Cl]2 (cod=1,5‐cyclooctadiene) and N‐benzhydryl‐N‐phenyldinaphthophosphoramidite (BHPphos), showed excellent control of both diastereo‐ and enantioselectivities.

Transition-metal-catalyzed asymmetric allylic dearomatization reactions.

Dearomatization reactions serve as powerful methods for the synthesis of highly functionalized, three-dimensional structures starting with simple planar aromatic compounds. Among processes of this type, catalytic asymmetric dearomatization (CADA) reactions are attractive owing to the large number of aromatic compounds that are readily available and the fact that they enable direct access to enantiopure polycycles and spirocycles, which frequently are key structural motifs in biologically active natural products and pharmaceuticals. However, as a consequence of their high stabilities, arenes only difficultly participate in dearomatization reactions that take place with high levels of enantioselectivity. Transition-metal-catalyzed asymmetric allylic substitution reactions have been demonstrated to be powerful methods for enantioselective formation of C-C and C-X (X = O, N, S, etc.) bonds. However, the scope of these processes has been explored mainly using soft carbon nucleophiles, some hard carbon nucleophiles such as enolates and preformed organometallic reagents, and heteroatom nucleophiles. Readily accessible aromatic compounds have been only rarely used directly as nucleophiles in these reactions. In this Account, we present the results of studies we have conducted aimed at the development of transition-metal-catalyzed asymmetric allylic dearomatization reactions. By utilizing this general process, we have devised methods for direct dearomatization of indoles, pyrroles, phenols, naphthols, pyridines, and pyrazines, which produce various highly functionalized structural motifs bearing all-carbon quaternary stereogenic centers in a straightforward manner. In mechanistic investigations of the dearomatization process, we found that the five-membered spiroindolenines serve as intermediates, which readily undergo stereospecific allylic migration to form corresponding tetrahydro-1H-carbazoles upon treatment with a catalytic amount of TsOH. It is worth noting that no notable loss of the enantiomeric excess of the spiroindolenine derivatives takes place during the rearrangement process as a consequence of the intervention of a "three-center-two-electron"-type transition state, a proposal that has gained support from the results of DFT calculations. Equally intriguing, upon tuning of the electronic nature of the tethers, pyrroles or indoles undergo unprecedented Ir or Ru catalyzed intramolecular allylic alkylation promoted dearomatization/migration reactions. The operation of this novel reaction pathway provides additional information leading to a greater mechanistic understanding of the transition-metal-catalyzed enantioselective intramolecular functionalizations of pyrroles and indoles. The combined results of this effort provide not only methods for the efficient synthesis of highly enantioenriched fused and spiro polycycles but also novel strategies in the field of asymmetric catalysis.

ChemInform Abstract: Total Synthesis of Cristatic Acid Based on Late‐Stage Decarboxylative Allylic Migration and Biomimetic Aromatization of a Diketo Dioxinone.

AbstractThe total synthesis of the title compound (I) including 15 linear steps is achieved in 2.7% overall yield.

Total Synthesis of Cristatic Acid Based on Late‐Stage Decarboxylative Allylic Migration and Biomimetic Aromatization of a Diketo Dioxinone

AbstractA fifteen‐step synthesis of methyl cristatate is described. tert‐Butyl‐[(E)‐6‐iodo‐3‐methylhex‐2‐enyloxy)]diphenylsilane, synthesized from geraniol, was coupled with 2‐(diethoxymethyl)‐4‐lithiofuran and transformed – by acetal hydrolysis, Wittig olefination, and desilylation – into a sesquiterpene furan alcohol. This alcohol was converted into methyl cristatate by sequential condensation with carbonyldiimidazole and the enolate dianion derived from 2,2‐dimethyl‐6‐(2‐oxopropyl)‐4H‐1,3‐dioxin‐4‐one and subsequent Pd0‐catalyzed decarboxylative allylic migration, biomimetic aromatization, and transesterification with methanol.

ChemInform Abstract: π‐Acid Mediated Insertion of Alkynes into Carbon—Heteroatom σ‐Bonds

AbstractReview: about 100 refs.

π-Acid Mediated Insertion of Alkynes into Carbon–Heteroatom σ-Bonds

The rapidly expanding field of gold and platinum π-acid catalysis has led to the discovery of diverse transformations that are initiated with nucleophilic attack onto a metal-activated alkyne. This review brings together those reactions which employ a heteroatom nucleophile bearing a functional group that can subsequently migrate to effect a formal insertion of the alkyne into a carbon–heteroatom­ σ-bond. This reactivity profile is encountered in a range of efficient and powerful cycloisomerisations for the preparation of carbo- and heterocycles. 1 Introduction 2 1,2-Addition of Carbon–Heteroatom Bonds across Alkynes 2.1 Heteroatom-to-Carbon Allyl Migrations 2.2 Accessing Sigmatropic Rearrangements 2.3 Related Palladium-Catalysed 1,2-Carboalkoxylations and Carboaminations 2.4 Beyond Allyl Migration in the 1,2-Carbofunctionalisation of Alkynes 2.5 Oxonium Ion Migration 2.6 Migrating Centres at Higher Oxidation Levels 2.7 Migration of Heteroatoms 3 1,5 Heteroatom-to-Carbon Migrations 3.1 Alkynyl Benzoates as Alkylating Agents 4 Internal versus External Migrations 4.1 Internal Migrations of Oxonium Species 5 1,1-Carbofunctionalisations 6 Application in Natural Products 7 Summary and Conclusions

ChemInform Abstract: Gold‐Catalyzed Heteroannulation and Allyl Migration: Synthesis of Highly Functionalized Indole Derivatives.

Highly substituted indole derivatives have been prepared in good to excellent yields by a novel gold-catalyzed cyclization accompanied by [3,3]-migration of the allyl strategy. We have been able to introduce an allyl group at the C1 position of pyrano[3,2-e]indol-6(7H)-one and pyrrolo[3,2-f]quinolin-7(6H)-one moieties that provide a scope for further transformation.

Gold-catalyzed heteroannulation and allyl migration: synthesis of highly functionalized indole derivatives

Highly substituted indole derivatives have been prepared in good to excellent yields by a novel gold-catalyzed cyclization accompanied by [3,3]-migration of the allyl strategy. We have been able to introduce an allyl group at the C1 position of pyrano[3,2- e]indol-6(7 H)-one and pyrrolo[3,2 -f]quinolin-7(6 H)-one moieties that provide a scope for further transformation.

Generation of 1-aryl-3-methoxycarbonylnitrilimines and their reactions with unsaturated hydrocarbons

Thermolysis of 1-(4-methoxyphenyl)- and 1-(4-fluorophenyl)heptamethoxycarbonyl-3a,7a-dihydroindazoles at 135–140 °C resulted in the elimination of hexamethyl benzenehexacarboxylate and in the generation of 1-aryl-3-methoxycarbonylnitrilimines, which were trapped by alkenes and dienes to give the corresponding (1) pyrazolines via 1,3-dipolar cycloaddition and (2) 2-oxoalken-1-oic acid hydrazones via allylic proton migration to the nitrogen atom. The reaction with tetramethylethene unexpectedly yielded substituted 5-(1-hydroxy-1-methylethyl)- or 5-acetylpyrazolinecarboxylates as the main products. The formation of the latter compounds suggests initial abstraction of the H atom from tetramethylethene and probable participation of a water molecule that supplies one more oxygen atom to the reaction products.