B(C6F5)3-catalyzed Prins/Ritter reaction: a novel synthesis of hexahydro-1H-furo[3,4-c]pyranyl amide derivatives

Ketones as strategic building blocks for the synthesis of natural product-inspired compounds

Natural product-inspired compound collections serve as excellent sources for the identification of new bioactive compounds to treat disease. However, such compounds must necessarily be more structurally-enriched than traditional screening compounds, therefore inventive synthetic strategies and reliable methods are needed to prepare them. Amongst the various possible starting materials that could be considered for the synthesis of natural product-inspired compounds, ketones can be especially valuable due to the vast variety of complexity-building synthetic transformations that they can take part in, their high prevalence as commercial building blocks, and relative ease of synthesis. With a view towards developing a unified synthetic strategy for the preparation of next generation bioactive compound collections, this review considers whether ketones could serve as general precursors in this regard, and summarises the opulence of synthetic transformations available for the annulation of natural product ring-systems to ketone starting materials.

Recent advances of Ritter reaction and its synthetic applications

This review provides a comprehensive survey of Ritter reactions from 2014 to 2020.

Tandem Prins cyclizations for the construction of oxygen containing heterocycles

Tandem Prins cyclization is a versatile method for the synthesis of fused/bridged/spirotetrahydropyran scaffolds. Therefore, it has become a powerful tool for the stereoselective synthesis of oxygen/nitrogen containing heterocycles. Indeed, previous review articles on Prins spirocyclization illustrate the synthesis of spirotetrahydropyran derivatives and the aza-Prins reaction demonstrates its application in the total synthesis of natural products. The current review is devoted specifically to highlight tandem Prins cyclizations for the construction of fused scaffolds and related frameworks with a particular emphasis on recent applications. The mechanistic aspects and the scope of the methods are briefly discussed herein.

Boron-Catalyzed O-H Bond Insertion of α-Aryl α-Diazoesters in Water

A catalytic, metal-free O-H bond insertion of α-diazoesters in water in the presence of B(C₆F₅)₃· nH₂O (2 mol %) was developed, affording a series of α-hydroxyesters in good to excellent yields. The reaction features easy operation and wide substrate scope, and importantly, no metal is needed as compared with the conventional methods. Significantly, this approach further expands the applications of B(C₆F₅)₃ under water-tolerant conditions.

B(C6F5)3 catalysed reduction of para-quinone methides and fuchsones to access unsymmetrical diaryl- and triarylmethanes: elaboration to beclobrate

An effective method for the synthesis of diaryl- and triarylmethane derivatives through a Lewis acid catalyzed reduction of para-quinone methides and fuchsones, respectively, using the Hantzsch ester as a hydride surrogate is described.

Three-Component, Diastereoselective Prins-Ritter Reaction for cis-Fused 4-Amidotetrahydropyrans toward a Precursor for Possible Neuronal Receptor Ligands

Here, we report an unprecedented, highly diastereoselective Prins-Ritter reaction of aldehydes, homoallylic alcohols, and nitriles in a three-component coupling reaction for the synthesis of tetra-cis-substituted 4-amidotetrahydropyrans. In this study, the reaction was not only applied for carbohydrate-based heterobicycles but also for more complex heterotricycles, showing acceptable levels of conversion yield (42-97% BRSM) and exclusive diastereoselectivity. Furthermore, the latter heterotricycles were converted to nine analogues of our neuronal receptor ligands IKM-159 and MC-27. An in vivo assay by intracerebroventricular injection in mice suggested that the substituent at C9 of the novel analogues interferes with the molecular interactions with the AMPA receptor, which was originally observed in the complex of IKM-159 and the GluA2 ligand binding domain. Our research has thus shown the power of a multicomponent coupling reaction for the preparation of a structurally diverse compound collection to study structure-activity relationships of biologically active small molecules.

B(C6F5)3 catalysed 1,6-conjugate allylation of para-quinone methides: expedient access to allyl diarylmethanes

An efficient protocol for the synthesis of unsymmetrical allyl diarylmethanes through a Lewis acid catalysed 1,6-conjugate addition of allylsilanes to para-quinone methides is described.

Synthesis of antiproliferative 13α-d-homoestrones via Lewis acid-promoted one-pot Prins-Ritter reactions of d-secosteroidal δ-alkenyl-aldehydes

A simple one-pot Prins-Ritter route was developed for the synthesis of 16-acylamino-17a-hydroxy-d-homoestrone 3-benzyl and 3-methyl ethers in the 13α-estrone series. The d-secosteroidal δ-alkenyl-aldehydes were allowed to react with different nitriles in the presence of BF3·OEt2 as a Lewis acid catalyst. Prins cyclizations afforded 17a-hydroxy-16-carbenium ions, which underwent Ritter reactions with nitriles, leading to 16α- or 16β-acylamino derivatives. A side-product in which a dihydro-1,3-oxazine was bridged to six-membered ring D at positions 16α,17aα was formed in each reaction. The antiproliferative properties of the novel 13α-d-homosteroids were determined on a panel of human adherent cancer cell lines (HeLa, MCF-7, T47D, MDA-MB-231, MDA-MB-361, A2780 and A431) by means of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assays. Some compounds proved to be more effective (with submicromolar IC50 values) than the reference agent cisplatin. One of the most potent compounds substantially increased the rate of tubulin polymerization. Cell cycle analyses by flow cytometry indicated a concentration-dependent accumulation of the G2/M cell population.