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

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

“…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 -cloud of the additive can stabilize, through p z - dispersion interactions, the transient biradicals of these sequences, thereby ensuring a faster conversion of the substrate.…”

Formation of Isolable Dearomatized [4 + 2] Cycloadducts from Benzenes, Naphthalenes, and N-Heterocycles Using 1,2-Dihydro-1,2,4,5-tetrazine-3,6-diones as Arenophiles under Visible Light Irradiation

“…Here, we report that 1,2-dihydro-1,2,4,5-tetrazine-3,6-diones (TETRAD; 3 ), the six-membered analogues of TADs, undergo visible-light-promoted [4 + 2] cycloaddition reactions − with benzenes, naphthalenes, and several N -heteroaromatic compounds, and the generated cycloadducts are stable enough to be isolated via chromatographic purification (Scheme c). The isolated adducts were characterized using single-crystal X-ray diffraction (XRD) and used for further transformation reactions at room temperature or above.…”

Photochemical Reduction of Quinolines with γ-Terpinene

“…Recently our lab, in collaboration with the Houk and Glorius groups, developed a dearomative cycloaddition reaction of quinolines and alkenes (Scheme ). − Based on our previous work and Morofuji/Kano’s work, the reaction is proposed to operate by triplet energy transfer to a Lewis/Brønsted acid activated quinoline, followed by stepwise cycloadditions with an alkene . The key intermediate in these reactions is proposed to be a triplet quinoline.…”