Ligand-Controlled Palladium-Catalyzed Carbonylation of Alkynols: Highly Selective Synthesis of α-Methylene-β-Lactones

Ag-Catalyzed Selective C-C Bond Activation of Cyclopropenones to Access α-Alkylidene Lactones

A novel Ag-catalyzed ring opening of unsymmetric cyclopropenones for the stereoselective synthesis of a diverse range of α-alkylidene lactones has been developed. In this protocol, two different C-C(O) bonds were distinguished, demonstrating selective C-C bond activation. This reaction features a wide substrate scope, good functional group compatibility, and high atom economy, providing a versatile and general approach to the construction of α-alkylidene lactones.

Syntheses and medicinal chemistry of spiro heterocyclic steroids

There is compelling evidence that incorporating a heterocyclic moiety into a steroid can alter its pharmacological and pharmacokinetic properties, driving intense interest in the synthesis of such hybrids among research groups. In this review, we present an overview of recent synthetic methodologies, spanning the period from 2000 to 2023, for the preparation of spiro heterocyclic steroids. The compounds surveyed encompass four-, five-, six-, and seven-membered heterocycles appended to various positions of steroidal backbones, with spirocycles containing oxygen, nitrogen, and sulfur atoms being predominant. The outlined synthetic procedures emphasize the pivotal steps for constructing the heterocycles, often accompanied by a detailed account of the overall synthesis pathway. The review encompasses innovative compounds, including bis-steroids linked by a spiro heterocycle and steroids conjugated to heterocyclic moieties containing three or more (hetero)cycles. Moreover, many compounds are accompanied by data on their biological activities, such as antiproliferative, antimalarial, antimicrobial, antifungal, steroid antagonist, and enzyme inhibition, among others, aimed at furnishing pertinent insights for the future design of more potent and selective drugs.

One-Step Electrocatalytic Approach Applied to the Synthesis of β-Propiolactones from CO2 and Dienes

β-Lactones are common substructures in a variety of natural products and drugs, and they serve as versatile synthetic intermediates in the production of valuable chemical derivatives. Traditional β-lactone synthesis relies on laborious multi-step synthetic methods that use toxic compounds, sophisticated catalysts, expensive, and/or reactive chemicals. Based on the in situ electrochemical formation of metal-based nanoclusters, this paper describes the development of a one-step, room temperature electrocatalytic method for the formation of stable β-lactone from CO₂ and dienes. This one-step "electrosynthesis" method results in the formation of a new class of β-lactone with high selectivity (up to 100%) and activity (up to 80% yields with respect to the reacted diene) by regulating the applied potential and current density. This work paves the way for more sustainable and environmentally friendly reaction pathways based on the in situ formation of nanoclusters as organic electrosynthesis catalysts.

Tropane-Based Dispirocyclic Oxiranes and Spirocyclic Ketones

The Prilezhaev epoxidation of N-Boc-protected 3-cyclobutylidenetropane 1a affords a 1:2 mixture of compounds 2a and 2b, in which tropane and cyclobutane fragments are spiro-connected to the oxirane ring in endo- and exo-fashion, respectively. The exo-isomer 2b is obtained in 89% yield and 97% selectivity via the dioxirane oxidation of 1a. BF3-catalyzed isomerization of exo-oxirane 2b results in a 1:1 mixture of the spirocyclic ketones endo 3a and exo 3b containing spiro-connected tropane and cyclopentanone rings, while endo-epoxide 2a gives exclusively endo-ketone 3a. Prilezhaev and dioxirane epoxidations of N-Boc-protected 3-cyclopropylidenetropane 1b affords a mixture of endo- and exo-oxiranes 2c and 2d. Compounds 2c and 2d are not isolated in individual forms since they isomerize into a mixture of spirocyclic ketones endo 3c and exo 3d. Removal of the Boc groups from ketones 3a–d gives the corresponding hydrochlorides of aminoketones 4a–d in quantitative yields. Quantum chemical calculations predict that the rearrangement of endo-epoxides into the corresponding endo-ketones involving BF3-containing intermediates has by 4.4–7.9 kcal/mol lower activation barriers than the respective conversion of the exo-epoxides into exo-ketones. The cyclopropyl-containing dispiroepoxides 2c and 2d are predicted to interconvert faster into the corresponding ketones compared to their less strained cyclobutyl counterparts 2a and 2b.

Room-temperature Pd-catalyzed methoxycarbonylation of terminal alkynes with high branched selectivity enabled by bisphosphine-picolinamide ligand

We report the room-temperature Pd-catalyzed methoxy-carbonylation with high branched selectivity using a new class of bisphosphine-picolinamide ligands. Systematic optimization of ligand structures and reaction conditions revealed the significance of both the picolinamide and bisphosphine groups in the ligand backbone. This strategic design of ligand was leveraged to deliver various α-substituted acrylates in good to excellent yields.

Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate.

Efficient Palladium-Catalyzed Carbonylation of 1,3-Dienes: Selective Synthesis of Adipates and Other Aliphatic Diesters

The dicarbonylation of 1,3‐butadiene to adipic acid derivatives offers the potential for a more cost‐efficient and environmentally benign industrial process. However, the complex reaction network of regioisomeric carbonylation and isomerization pathways, make a selective and direct transformation particularly difficult. Here, we report surprising solvent effects on this palladium‐catalysed process in the presence of 1,2‐bis‐di‐tert‐butylphosphin‐oxylene (dtbpx) ligands, which allow adipate diester formation from 1,3‐butadiene, carbon monoxide, and methanol with 97 % selectivity and 100 % atom‐economy under scalable conditions. Under optimal conditions a variety of di‐ and triesters from 1,2‐ and 1,3‐dienes can be obtained in good to excellent yields.

Ligand-Controlled Palladium-Catalyzed Carbonylation of Alkynols: Highly Selective Synthesis of α-Methylene-β-Lactones

The first general and regioselective Pd-catalyzed cyclocarbonylation to give α-methylene-β-lactones is reported. Key to the success for this process is the use of a specific sterically demanding phosphine ligand based on N-arylated imidazole (L11) in the presence of Pd(MeCN)2 Cl2 as pre-catalyst. A variety of easily available alkynols provide under additive-free conditions the corresponding α-methylene-β-lactones in moderate to good yields with excellent regio- and diastereoselectivity. The applicability of this novel methodology is showcased by the direct carbonylation of biologically active molecules including natural products.