Methylene Blue as a Photosensitizer and Redox Agent: Synthesis of 5‐Hydroxy‐1H‐pyrrol‐2(5H)‐ones from Furans

Abstract

A highly efficient and general singlet-oxygen-initiated one-pot transformation of readily accessible furans into 5-hydroxy-1H-pyrrol-2(5H)-ones has been developed. The methodology was extended to the synthesis of other high-value α,β-unsaturated γ-lactams. This useful set of transformations relies not only on the photosensitizing ability of methylene blue, but also on its redox properties: properties that have until now been virtually ignored in a synthetic context.

Oxidative Dearomatization of 4,5,6,7‐Tetrahydro‐1H‐indoles Obtained by Metal‐ and Solvent‐Free Thermal 5‐endo‐dig Cyclization: The Route to Erythrina and Lycorine Alkaloids

“…The reasonsf or the poor scalability of DMP-oxidation on as cale larger than 10 mmol are the subject of further investigations. The acquiremento f3g, 3i,a nd 3j completed the formal total syntheses of aw hole pleiad of alkaloid structures, [17] namely (AE)-3-demethoxy-1,2-dihydroerysotramidine and (AE)-3demethoxy-1,2-dihydroerythraline, [3e] (AE)-erysotramidine, [3d] which could be furthert ransformed into (AE)-erysotrine [18a] and (AE)-erythravine, [18b] and finally,( AE)-g-lycorane [3b] (Scheme 3). To achieve another formal synthesis of the rearranged alkaloid tetrahydroerythraline, hexahydroapoerysopined imethyl ether [19] indolone 3k was subjected to intramolecular ligand-free Heck cyclization under Jeffery conditions.…”

Singlet Oxygen and Dyes: Synthesis with Visible Light is Where the Future Lies

“…By dual role sequences, we mean photocatalysts or dyes that fulfill two roles at different stages of the sequence – using light switches to access even more reaction pathways. We hope to develop sequences which have both energy transfer and electron transfer steps in order to controllably access a yet more diverse array of privileged scaffolds through one pot operations …”

Asymmetric and Site-Selective [3 + 2]-Annulations for the Synthesis of High-Value Bicyclic Lactams

“…12 We envisioned that the resultant lactams 13 might serve as versatile reaction partners via controlled reaction at any one of their multiple nucleophilic positions. It was hoped that they might be partnered with dielectrophilic α,β-unsaturated aldehydes activated through iminium ion catalysis.…”

“…12,13 Purified 2a was then subjected to various conditions using LUMO-lowering catalysts I – III (cat. I – III ) and cinnamaldehyde ( 4a ).…”

“…N -Benzyl-2-pyrrolidinone 3a was synthesized using the singlet oxygen based protocol 12,13 and, subsequently, treated with 1.5 equiv of cinnamaldehyde ( 4a ) and 10% of cat. I in DCE (conditions I, Scheme 3).…”