Palladium-catalyzed synthesis of N-vinyl pyrroles and indoles

An Efficient One-Pot Synthesis of 5-Sulfanyl-1-[2-(vinyloxy)ethyl]-1H-pyrrol-2-amines as Precursors of 1-Vinylpyrroles

Sequential processing of monolithiated tertiary propargylamines with 2-(vinyloxy)ethyl isothiocyanate and t-BuOK–DMSO results in the introduction of a highly reactive 2-(vinyloxy)ethyl group at the position 1 of the pyrrole ring thus formed. In this way, a series of new 5-sulfanyl-1-[2-(vinyloxy)ethyl]-1H-pyrrol-2-amines were obtained in a yield of up to 92%. The latter in the presence of t-BuOK–DMSO system (110–120 °C, 10–15 min) eliminates vinyl alcohol to give rare-functionalized 1-vinylpyrroles, namely 5-sulfanyl-1-vinyl-1H-pyrrol-2-amines, inaccessible by the known methods.

Formation of XPhos-Ligated Palladium(0) Complexes and Reactivity in Oxidative Additions

Understanding the nature of the intermediate species operating within a palladium catalytic cycle is crucial for developing efficient cross-coupling reactions. Even though the XPhos/Pd(OAc)₂ catalytic system has found numerous applications, the nature of the active catalytic species remains elusive. A Pd⁰ complex ligated to XPhos has been detected and characterized in situ for the first time using cyclic voltammetry and NMR techniques. In the presence of XPhos, Pd(OAc)₂ initially associates with the ligand to form a complex in solution, which has been characterized as Pd^II (OAc)₂ (XPhos). This Pd^II center is then reduced to the Pd⁰ (XPhos)₂ species by an intramolecular process. This study also sheds light on the formation of Pd^I -Pd^I dimers. Finally, a kinetic study probes a dissociative mechanism for the oxidative addition with aryl halides involving Pd⁰ (XPhos) as the reactive species in equilibrium with the unreactive Pd⁰ (XPhos)₂ . Remarkably, the reportedly poorly reactive PhCl reacts at room temperature in the oxidative addition, which confirms the crucial role of the XPhos ligand in the activation of aryl chlorides.

Heterogeneous Gold(III)-Catalysed Double Hydroamination of 2-Alkynylanilines with Terminal Alkynes Leading to N-Vinylindoles

Heterogeneous double hydroamination of 2-alkynylanilines with terminal alkynes was achieved by using a magnetic nanoparticles-supported gold(III)-2,2′-bipyridine complex and silver trifluoromethanesulfonate as catalysts to afford the corresponding N-vinylindoles in moderate to good yields under mild and solvent-free conditions. The heterogeneous gold catalyst can easily be separated from the reaction mixture by simply applying an external magnet and can be recycled up to seven times without significant loss of activity.

Pd-Catalyzed Alkene Carboheteroarylation Reactions for the Synthesis of 3-Cyclopentylindole Derivatives

The Pd-catalyzed alkene carboheteroarylation of aryl and alkenyl triflate electrophiles bearing pendant alkenes with heteroaromatic nucleophiles affords substituted carbocycles with 3-indolyl or 3-pyrrolyl groups. The products are obtained in moderate to good yields, and the use of alkenyl triflate substrates produces products with high diastereoselectivities. The transformation is believed to proceed via a Friedel-Crafts-like reaction between the heteroaromatic nucleophile and an intermediate electrophilic palladium complex.

Synthesis of N-vinylindoles through copper catalyzed cyclization reaction of N-(2-alkynylphenyl)imine

A Cu(ii)-catalyzed cyclization reaction of N-(2-alkynylphenyl)imine to synthesize substituted N-vinylindoles is developed.

A Simple Synthesis of N-Vinylpyrrole, N-vinylindole and N-Vinylcarbazole Derivatives

Reaction of pyrrole, indole or carbazole with dialkyl acetylenedicarboxylates catalysed by N-methylimidazole provides a simple and efficient route for the synthesis of N-vinylpyrrole, N-vinylindole and N-vinylcarbazole derivatives in high yields.

Dialkylbiaryl Phosphines in Pd-Catalyzed Amination: A User's Guide

Dialkylbiaryl phosphines are a valuable class of ligand for Pd-catalyzed amination reactions and have been applied in a range of contexts. This review attempts to aid the reader in the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations.

Diamine Ligands in Copper-Catalyzed Reactions

The utility of copper-mediated cross-coupling reactions has been significantly increased by the development of mild reaction conditions and the ability to employ catalytic amounts of copper. The use of diamine-based ligands has been important in these advances and in this review we discuss these systems, including the choice of reaction conditions and applications in the synthesis of pharmaceuticals, natural products and designed materials.

Total synthesis and study of myrmicarin alkaloids

The myrmicarins are a family of air- and temperature-sensitive alkaloids that possess unique structural features. Our concise enantioselective synthesis of the tricyclic myrmicarins enabled evaluation of a potentially biomimetic assembly of the complex members via direct dimerization of simpler structures. These studies revealed that myrmicarin 215B undergoes efficient and highly diastereoselective Brønsted acid-induced dimerization to generate a new heptacyclic structure, isomyrmicarin 430A. Mechanistic analysis demonstrated that heterodimerization between myrmicarin 215B and a conformationally restricted azafulvenium ion precursor afforded a functionalized isomyrmicarin 430A structure in a manner that was consistent with a highly efficient, non-concerted ionic process. Recent advancement in heterodimerization between tricyclic derivatives has enabled the preparation of strategically functionalized hexacyclic structures. The design and synthesis of structurally versatile dimeric compounds has greatly facilitated manipulation of these structures en route to more complex myrmicarin derivatives.

Stereoselective synthesis of acetoacetate-derived enol triflates

A highly stereoselective method for preparing ( Z)- and ( E)-enol triflates derived from substituted acetoacetate derivatives is described. The salient feature of this methodology is the use of Schotten-Baumann-type conditions to control enolate geometry using either aqueous LiOH ( Z-selective) or aqueous (Me)(4)NOH ( E-selective) in combination with triflic anhydride to provide a practical and predictable approach to these valuable substrates.

Biaryl phosphane ligands in palladium-catalyzed amination

Palladium-catalyzed amination reactions of aryl halides have undergone rapid development in the last 12 years, largely driven by the implementation of new classes of ligands. Biaryl phosphanes have proven to provide especially active catalysts in this context. This Review discusses the application of these catalysts in C-N cross-coupling reactions in the synthesis of heterocycles and pharmaceuticals, in materials science, and in natural product synthesis.

Internal azomethine ylide cycloaddition methodology for access to the substitution pattern of aziridinomitosene A

Highly substituted, tethered alkyne dipolarophiles participate in the internal 2 + 3 cycloaddition with azomethine ylides generated by treatment of oxazolium salts with cyanide ion. Starting from oxazole 26, a sequence of N-methylation, cyanide addition, and electrocyclic ring opening of a 4-oxazoline intermediate affords the indoloquinone 31 in a one-pot process. A similar reaction from the protected alkynol derivative 25 affords the sensitive, but isolable, enone 32, and subsequent oxidation affords 31 and the deprotected quinone alcohol 34. Related azomethine cycloaddition methodology via intramolecular oxazolium salt formation from 43 or 46 is also demonstrated and allows the synthesis of quinone 45 and derived structures having the substitution pattern of aziridinomitosene A. Removal of the N-trityl protecting group could not be achieved without aziridine cleavage.

Palladium-Catalyzed α-Vinylation of Carbonyl Compounds

A mild, general, catalytic system for the alpha-vinylation of carbonyl compounds has been developed. By employing [Pd(P(t)Bu(3))Br](2) as catalyst and LHMDS as base, vinyl bromides, vinyl triflates, and vinyl tosylates couple with 3-methyloxindole in satisfactory yields. The same catalytic system is extended to the alpha-vinylation of ketones and esters.

Gold(III)-Catalyzed Double Hydroamination of o-Alkynylaniline with Terminal Alkynes Leading to N-Vinylindoles

A highly efficient double-hydroamination reaction of o-alkynylanilines with terminal alkynes leading to N-alkenylindoles was developed by using gold(III) as a catalyst under neat conditions. [reaction: see text].

Dimerization of (+)-Myrmicarin 215B. A Potential Biomimetic Approach to Complex Myrmicarin Alkaloids

The acid promoted diastereoselective dimerization of myrmicarin 215B is described. The reactivity of these sensitive alkaloids, structural assignment, and a possible mechanism for the observed dimerization are discussed. These finding raise the intriguing possibility of the synthesis of the highly sensitive myrmicarin alkaloids based on a strategy involving the direct dimerization of functional tricyclic myrmicarin derivatives.