Synthesis of Enantioenriched gem-Disubstituted 4-Imidazolidinones by Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation

Pd-Catalysed asymmetric allylic alkylation of heterocycles: a user's guide

This review provides an in-depth analysis of recent advances and strategies employed in the Pd-catalysed asymmetric allylic alkylation (Pd-AAA) of nucleophilic prochiral heterocycles. The review is divided into sections each focused on a specific family of heterocycle, where optimisation data and reaction scope have been carefully analysed in order to bring forward specific reactivity and selectivity trends. The review eventually opens on how computer-based technologies could be used to predict an ideally matched catalytic system for any given substrate. This user-guide targets chemists from all horizons interested in running a Pd-AAA reaction for the preparation of highly enantioenriched heterocyclic compounds.

Synthesis of Polycyclic Imidazolidinones via Cascade [3 + 2]-Annulation of β-Oxo-acrylamides with Cyclic N-Sulfonyl Imines

An Et3N-catalyzed cascade [3 + 2]-annulation of β-oxo-acrylamides with cyclic N-sulfonyl ketimines or sulfamate-derived imines is developed under mild reaction conditions, which provides a concise and efficient route to access valuable sultam- or sulfamidate-fused imidazolidinone derivatives in good to excellent yields (80-95% yields) with excellent diastereoselectivities (>20:1 drs). The current protocol features atom economy, a transition-metal-free process, and broad functional group tolerance. Moreover, the asymmetric variant of the [3 + 2]-cycloaddition reaction was achieved in the presence of diphenylethanediamine or quinine-based bifunctional squaramide organocatalysts C-1 and C-11, giving the corresponding chiral polycyclic imidazolidinones in 68-90% yields with 25-94% ees and >20:1 drs in all cases.

Support studies toward the hicksoane alkaloids reveal cascade reactions of a (tryptophanamido)methylglycinate

Herein we report unanticipated results that emerged from a synthetic study targeting the unique triazocane present in the hicksoane alkaloids. An initial strategy focused on the cyclisation-ring expansion of a 3-(tryptophyl)imidazolidin-4-one failed due to the high reactivity of the imide unit; passing a methanolic solution of this compound through a weakly basic ion exchange resin led to methanolysis to form a (tryptophanamido)methylglycinate. Attempted lactamisation of this (tryptophanamido)methylglycinate led to the formation of a (tryptophyl)imidazolidin-4-one, a rare imidazopyrido[3,4-b]indolone and a β-carboline. Control reactions informed a mechanistic rationale for these cascade processes.

Palladium-Catalyzed Asymmetric Conjugate Addition of Arylboronic Acids to α,β-Unsaturated Lactams: Enantioselective Construction of All-Carbon Quaternary Stereocenters in Saturated Nitrogen-Containing Heterocycles

Stereogenic nitrogen-containing heterocycles are ubiquitous in natural products and pharmaceutical compounds, but methods for their enantioselective construction have remained elusive. We report a general method for the asymmetric conjugate addition of arylboronic acids to β-alkyl/aryl α,β-unsaturated lactams that affords chiral β,β-disubstituted lactams. The transformation is operationally simple and air- and moisture-tolerant and uses a commercially available (S)-t-Bu-PyOx ligand. The method is high-yielding (up to 95% yield) and enantioselective (up to 97% ee) for a wide range of arylboronic acids and α,β-unsaturated lactams, including those with different ring sizes.

Catalytic Enantioselective Synthesis of α-Difunctionalized Cyclic Sulfones

As saturated heterocyclic building blocks become increasingly popular in medicinal chemistry and drug discovery programs, expansion of the synthetic toolkit to novel stereofunctionalized heterocycles is a priority. Herein, we report the development of a palladium-catalyzed decarboxylative asymmetric allylic alkylation reaction to access a broad range of enantioenriched α-difunctionalized 5- and 6-membered sulfones from easily accessible racemic starting materials. The allylic alkylation step was found to occur with high levels of enantioselectivity as a result of a palladium-mediated dynamic kinetic resolution of E/Z enolate intermediates. This methodology paves the way to hitherto unexplored stereodefined cyclic sulfones for medicinal chemistry applications.

The total synthesis of -strempeliopine via palladium-catalyzed decarboxylative asymmetric allylic alkylation

In the work reported herein, the concise and enantioselective total synthesis of the Schizozygine alkaloid (-)-strempeliopine was developed. This synthetic strategy featured the palladium-catalyzed decarboxylative asymmetric allylic alkylation of N-benzoyl lactam to set up the absolute configuration at the C20 position, a highly diastereoselective one-pot Bischler-Napieralski/lactamization and iminium reduction sequence for the construction of the pentacyclic core structure, and the late-stage dearomative addition of indole, leading to the otherwise difficult-to-achieve hexacyclic indoline framework with complete control of four neighbouring stereocenters.

Palladium-Catalyzed Decarboxylative Asymmetric Allylic Alkylation of Thietane 1,1-Dioxides

A palladium-catalyzed decarboxylative asymmetric allylic alkylation of thietane 1,1-dioxides via linear enolate intermediates from racemic starting materials has been developed. This process installs an α-sulfonyl tetrasubstituted stereogenic center with high enantioselectivity. The potential to transform the alkylated products to novel types of enantioenriched spirocycles for medicinal chemistry applications has also been demonstrated.