Visible‐Light Promoted Intramolecular para‐Cycloadditions on Simple Aromatics

Abstract

Dearomative cycloadditions are a powerful tool to access a large chemical space exploiting simple and ubiquitous building blocks. The energetic burden due to the loss of aromaticity has however greatly limited their synthetic potential. We devised a general intramolecular method that overcomes these limitations thanks to the photosensitization of allenamides. The visible‐light‐promoted process gives complex [2.2.2]‐(hetero)‐bicyclooctadienes at room temperature, likely through the stabilization of transient (bi)radicals by naphthalene. The reaction tolerates several valuable functionalities, offering a convenient handle for a myriad of applications, including original isoindoles and metal complexes.

A Complementary Route for Alkene–Arene para-Cycloadditions by Visible-Light-Promoted Triplet Sensitization of Allenamides

“…We carried out detailed DFT studies to rationalize the role of naphthalene. 23 The reaction of both 1a and 1b was modeled at the M06/Def2-TZVP 27 level using DMF as the implicit solvent 28 and adding Grimme’s D3 dispersion corrections. 29 These analyses suggested that the extended π-cloud of the additive can stabilize, through p z –π dispersion interactions, the transient biradicals of these sequences, thereby ensuring a faster conversion of the substrate.…”

“…We recently reported a complementary approach that is based on the activation of the double-bond partner instead (Scheme 3b ). 23 The general method allows one to achieve dearomative para -cycloaddition between the terminal C=C double bond of an allenamide and simple, electronically unbiased, (het)aromatic rings. The work arose from the observation that N -acyl allenamides could be activated by energy transfer in the presence of an Ir(III) photocatalyst and visible light.…”

Construction of a Bicyclo[2.2.2]octene Skeleton via a Visible-Light-Mediated Radical Cascade Reaction of Amino Acid Derivatives with N-(2-Phenyl)benzoyl Groups

“…18−20 You et al developed an intramolecular double-dearomative reaction of indole deriva-tives bearing a pendant naphthyl ring via photocatalytic EnT processes. 21 More recently, the intramolecular para-cycloadditions on simple arenes using Ir(ppy) 3 have been developed by Maestri et al 22 In contrast, there are still limited examples of the construction of bridged polycycles via radical cascades triggered by visible-light-mediated photocatalytic SET processes. In 2019, Jiang and co-workers reported a photoredoxcatalyzed formal [3 + 2] cycloaddition of N-aryl-α-amino acids with isoquinoline N-oxides.…”