Domino dehydration/intermolecular (enantioselective) ketone-ene reactions catalysed by a simple solid in batch and in flow

The intermolecular carbonyl-ene reaction of ketones is still considered a challenge in organic chemistry, particularly with reusable solid catalysts, and implemented in a domino reaction. Herein, we show that the extremely cheap and non-toxic solid salt MgCl2 catalyzes the reaction of trifluoromethyl pyruvates not only during the conventional carbonyl-ene reaction with various aromatic and alkyl alkenes (in very high yields, up to >99%) but also in a domino reaction with the corresponding alcohols (precursors to the alkenes) in similar good yields. The solid can be reused in both cases without any erosion of the catalytic activity and can be employed in an in-flow process to maximize the reaction throughput. Besides, the reaction can be performed under solventless reaction conditions. Addition of a catalytic amount of chiral binaphthyl hydrogen phosphate allows carrying out the reaction with a reasonable enantiomeric excess (up to >70%) and in flow, in a rare example of enantioselective solid-catalyzed domino carbonyl-ene reaction using a cheap, simple, readily available and physically mixed catalytic solid. The MgCl2-catalytic system is also active in the industrially relevant citronellal-to-isopulegol carbonyl-ene reaction. These results pave the way to design sustainable domino carbonyl-ene reactions with extremely cheap solid catalysts.

Synthesis of 2-hydroxytetrahydrofurans by Wacker-type oxidation of 1,1-disubstituted alkenes

1,1-Disubstituted alkenes feature high steric hindrance, which renders their Wacker-type oxidation difficult. We demonstrate the stereoselective synthesis of 2-hydroxytetrahydrofurans via the Wacker-type oxidation of 3-methyl-3-buten-1-ols by using a PdCl₂(MeCN)₂/NO/BQ catalyst system under 1 atm O₂ in H₂O or H₂O/DMF.

Direct Synthesis of Bicyclic Acetals via Visible Light Catalysis

Polysubstituted bicyclic acetals are a class of privileged pharmacophores with a unique 3D structure and an adjacent pair of hydrogen bond acceptors. The key, fused acetal functionality is often assembled, via intramolecular cyclization, from linear substrates that are not readily available. Herein, we report a formal cycloaddition between cinnamyl alcohols and cyclic enol ethers under ambient photoredox catalysis conditions. Polysubstituted bicyclic acetals can be prepared in one step from readily available building blocks. Employment of sugar-derived enol ethers allows easy access to a library of scaffolds with intriguing conformation and medicinal chemistry potential.

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Synergistic catalysis of photocatalyst and HAT reagent

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5/5, 5/6, 5/7, 6/6 bicyclic acetals and polysubstituted THF formed in one step

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High stability of bicyclic acetal in SIF and SGF

Catalytic intramolecular carbonyl–ene reaction with ketones: evidence for a retro–ene process

The ene and reverse ene-processes occur with ketones, as shown by control experiments and by ESI-MS analysis.