A Pd-Catalyzed Synthesis of Functionalized Piperidines

Cycloadditions of 5-Vinyloxazolidine-2,4-diones: A Straightforward Access to the (Thio)hydantoin Scaffold

A palladium-catalyzed (3 + 2) cycloaddition between 5-vinyloxazolidine-2,4-diones (VOxD) and (thio)isocyanates is described. Under optimized conditions, an array of (thio)hydantoins was readily prepared, and an enantioselective version of this transformation was then studied. To illustrate the importance of this method, a concise synthesis of two bioactive compounds, nirvanol and mephenytoin, was carried out. This work emphasizes the synthetic potential of VOxD as useful precursors of zwitterionic aza-π-allylpalladiumII intermediates.

Palladium-Catalyzed Cycloaddition Reactions of π-Allylpalladium 1,4-Dipoles with 1,3,5-Triazinanes: Access to Hexahydropyrimidines, 1,3-Oxazinanes, and 1,5-Diazocanes

Palladium-catalyzed decarboxylation of 5-methylene-1,3-oxazinan-2-ones and 5-methylene-1,3-dioxan-2-ones to generate aza-π-allylpalladium and oxa-π-allylpalladium 1,4-dipoles for [4 + 2] cycloaddition reaction with 1,3,5-triazinanes was developed, affording a wide range of hexahydropyrimidine and 1,3-oxazinane derivatives in good to excellent yields (up to 99%). The acyclic sulfonamido-substituted allylic carbonates as aza-π-allylpalladium 1,4-dipole precursors also apply to the developed synthesized strategy, achieving the synthesis of hexahydropyrimidines. Moreover, the in situ-generated aza-π-allylpalladium 1,4-dipoles undergoing dimeric [4 + 4] cycloaddition were also demonstrated by the construction of 1,5-diazocane derivatives.

A Pd-Catalyzed Annulation Strategy to Linearly Fused Functionalized N-Heterocycles

Linearly fused polycyclic piperidines represent common substructures in natural products and biologically active small molecules. We have devised a Pd-catalyzed annulation strategy to these compounds that converts readily available 2-tetralones and indanones into these scaffolds with the potential for control of both enantio- and diastereoselectivity. Importantly, these compounds can be chemoselectively functionalized, providing an efficient and robust methodology to these important nitrogen-containing molecules.

Palladium-Catalyzed Ligand-Directed Divergent Decarboxylative Cycloadditions of Vinyloxazolidine-2,4-diones with 1,3,5-Triazinanes

This study demonstrates a highly efficient regiodivergent ligand-controlled palladium-catalyzed cycloaddition reaction of vinyloxazolidine-2,4-diones with 1,3,5-triazinanes. In the presence of a diphosphine ligand, the reaction proceeds via a (5+2) cycloaddition pathway to afford 1,3-diazepin-4-ones in excellent yields, while using a monophosphine ligand, the reaction proceeds smoothly via a (3+2) cycloaddition pathway to give imidazolidin-4-ones in good yields.

Pd-Catalyzed [4 + 1] Annulation Strategy to Functionalized 4-Methyleneproline Derivatives

A Pd-catalyzed formal [4 + 1] cycloaddition reaction of sulfur ylides and in situ-generated Pd-stabilized zwitterions offers a convenient route to a series of functionalized proline derivatives. The utility of this method is demonstrated by a gram-scale synthesis and chemoselective functionalization of a proline-based derivative.

Diastereo- and Enantioselective Palladium-Catalyzed Cycloadditions of 5-Vinyloxazolidine-2,4-diones with Electrophilic Imines

Despite the importance of the 4-imidazolidinone scaffold in bioactive compounds or organocatalysts, methodologies to access these nitrogenated heterocycles remain scarce. This manuscript describes a novel preparation of 4-imidazolidinones via a diastereo- and enantioselective (3 + 2) cycloaddition between 5-vinyloxazolidine-2,4-diones (VOxD) and electrophilic imines under palladium catalysis. This work supports the synthetic potential of VOxD as a promising equivalent of the C-C(═O)-N synthon.

Asymmetric Synthesis of Functionalizable Type II β-Turn-Inducing α-Amino Acid Building Blocks

Peptidomimetics are emerging as a promising class of potent and selective therapeutics. Among the current approaches to these compounds, the utilization of constrained lactams is a key element in enforcing the active peptide conformation, and the development of efficient and stereocontrolled methods for generating such lactam building blocks is an important objective. Current methods typically rely on the elaboration of existing α-amino acids, and in so doing, the side chain is sacrificed during the ring-forming process. We report a new asymmetric approach to lactam-constrained α-amino acid building blocks bearing a range of polar and hydrophobic side chains. The chemistry is amenable to rapidly generating di- and tripeptides, and the potential for these lactams to stabilize type II β-turns is demonstrated in the synthesis of the melanocyte-inhibiting factor peptidomimetic.

Palladium-Catalyzed Asymmetric (3 + 2) Cycloaddition of 5-Allenyloxazolidine-2,4-Diones with Barbiturate-Derived Alkenes: Synthesis of Spirobarbiturate-γ-Lactams

The 5-allenyloxazolidine-2,4-diones had been synthesized as novel precursors of π-allyl palladium zwitterion and were applied in a palladium-catalyzed enantioselective (3 + 2) annulation by using barbiturate-derived alkenes as the reaction partner in the presence of an axially chiral phosphoramidite ligand. This reaction proceeded smoothly under mild reaction conditions, affording highly functionalized spirobarbiturate-γ-lactam derivatives in excellent yields along with high diastereo- and enantioselectivities. The scale-up reaction and further transformation of the product were also successful.

Fungicide-inspired precursors of π-allylpalladium intermediates for palladium-catalyzed decarboxylative cycloadditions

Inspired by a fungicide, we designed 5-vinyloxazolidine-2,4-diones as new precursors of π-allylpalladium zwitterionic intermediates and developed palladium-catalyzed asymmetric (5 + 3) cycloaddition with azomethine imines and (3 + 2) cycloaddition with 1,1-dicyanoalkenes. Both reactions proceeded smoothly under mild reaction conditions to produce various chiral heterocyclic compounds in high yields with excellent enantioselectivities. These results revealed that 5-vinyloxazolidine-2,4-diones were a type of suitable precursor for palladium catalysis and will find extensive applications in Pd-catalyzed reactions such as cycloaddition and allylic alkylation.

Rh(III)-Catalyzed Synthesis of Amino-isocoumarins with N-Functionalized Cyclic Carbonates via C-H/O-H Annulation

A practical method to access amino-isocoumarins catalyzed by a Rh(III) complex through redox-neutral C-H/O-H annulation has been disclosed. The use of N-functionalized cyclic carbonates is crucial to facilitate the catalytic turnover, and a broad spectrum of amino-isocoumarin derivatives were prepared with satisfactory yields. Amino-isocoumarin estrone conjugated with a selenocyano functionality was identified to be nearly four times as active as the marketed drug abiraterone against T47D cancer cells.

A new type of δ-vinylvalerolactone for palladium-catalyzed cycloaddition: synthesis of nine-membered heterocycles

In this paper, a new type of δ-vinylvalerolactone was designed and synthesized, and used as a new precursor in Pd-catalyzed [6+3] cycloaddition with azomethine imines, leading to nine-membered 1,2-dinitrogen-containing heterocycles in 77-98% yields with >20 : 1 d.r. These nine-membered ring-fused products were further transformed into unusual tetracyclic bridged-ring compounds without loss of the diastereoselectivities.

Pd-Catalyzed [4 + 2] cycloaddition of methylene cyclic carbamates with dihydropyrazolone-derived alkenes: synthesis of spiropyrazolones

In this paper, a palladium-catalyzed [4 + 2] cycloaddition of 5-methylene-1,3-oxazinan-2-ones with 4-arylidene-2,4-dihydro-3H-pyrazol-3-ones has been developed to produce spiropyrazolones in high yields with excellent diastereoselectivities in nearly all cases. The cycloaddition reaction was scaled-up without significant loss of yield, and its synthetic utility has been demonstrated by further transformations of the products. The reaction type of N-Ts cyclic carbamates under palladium catalysis was extended to include [4 + 2] cycloaddition for the first time.

A Pd-Catalyzed [4 + 2] Annulation Approach to Fluorinated N-Heterocycles

3-Fluoro- and trifluoromethylthio-piperidines represent important building blocks for discovery chemistry. We report a simple and efficient method to access analogs of these compounds that are armed with rich functionality allowing them to be chemoselectively derivatized with high diastereocontrol.

Vinylcyclopropanes as All-Carbon 1,5-Dipoles: A Reactivity Switch for Palladium-Catalyzed (5 + 4) Cycloadditions

Azonanes were prepared by a palladium-catalyzed (5 + 4) cycloaddition between activated vinylcyclopropanes and 1-azadienes. During this process, the vinylcyclopropane partner displayed an unusual reactivity and behaved as an all-carbon 1,5-dipole. A N,N-bidentate ligand was required to inhibit the formation of thermodynamic (3 + 2) cycloadducts.

Strategies for the synthesis of spiropiperidines - a review of the last 10 years

Spiropiperidines have gained in popularity in drug discovery programmes as medicinal chemists explore new areas of three-dimensional chemical space. This review focuses on the methodology used for the construction of 2-, 3- and 4-spiropiperidines, covering the literature from the last 10 years. It classifies the synthesis of each of the types of spiropiperidine by synthetic strategy: the formation of the spiro-ring on a preformed piperidine ring, and the formation of the piperidine ring on a preformed carbo- or heterocyclic ring. While 3- and 4-spiropiperidines are predominantly synthesised for drug discovery projects, 2-spiropiperidines are synthesised en route to natural products. The lack of 2-spiropiperidines in drug discovery is presumably due to limited general procedures for their synthesis.

Kinetic resolution of 2,2-disubstituted-1,3-diketones via carbene catalysis

Organocatalytic kinetic resolution of 1,3-diketones with central quaternary stereocenters was achieved for the first time. The resolution proceeds via two basic modes, and the inherent principles between the different combinations of ketone groups and the resolution patterns were also disclosed.