Merging [2+2] Cycloaddition with Radical 1,4‐Addition: Metal‐Free Access to Functionalized Cyclobuta[a]naphthalen‐4‐ols

Abstract

A metal‐free [2+2] cycloaddition and 1,4‐addition sequence induced by S‐centered radicals has been achieved by treating benzene‐linked allene‐ynes with aryldiazonium tetrafluoroborates and DABCO‐bis(sulfur dioxide) in a one‐pot procedure. The reaction provides a greener and more practical access to functionalized cyclobuta[a]naphthalen‐4‐ols with valuable applications. More than 50 examples are demonstrated with excellent diastereoselectivity and chemical yields. The reaction pathway is proposed to proceed by the following steps:[2+2] cycloaddition, insertion of SO2, 1,4‐addition, diazotization, and tautomerization.

Tandem Anionic oxy‐Cope Rearrangement/Oxygenation Reactions as a Versatile Method for Approaching Diverse Scaffolds

“…[12] Whereas the resulting rearranged metal enolate has been previously subject to further polar reaction steps, such as a-alkylation, a-selenylation, a-hydroxylation, O-acetylation, silylation, or transannular aldol reactions, [12] tandem processes merging these pericyclic with radical reactions have so far remained elusive; to the best of our knowledge, only one example combining a [2+2] cycloaddition or a Claisen rearrangement with radical addition has been reported. [13] Scheme 1. Strategic combination of pericyclic rearrangements with radical a-oxygenation and new PRE-based 5-endo-trig cyclization reactions to approach cyclopentanes.…”

Tandemreaktionen aus anionischer Oxy‐Cope‐Umlagerung und Oxygenierung als vielseitiger Zugang zu verschiedenartigen Gerüsten

“…[12] Das resultierende umgelagerte Enolat wurde bisher in weiteren polaren Reaktionsschritten wie a-Alkylierung, a-Selenylierung, a-Hydroxylierung, O-Acetylierung, Silylierung oder transannularer Al-dolreaktion genutzt, [12] hingegen sind Tandemprozesse unbekannt, die pericyclische mit Radikalreaktionen verknüpfen; nur Beispiele einer [2+2]-Cycloaddition oder Claisen-Umlagerung in Verbindung mit Radikaladditionen wurden berichtet. [13] Wir zeigen hier Verknüpfungen von AOC der Dienole 3 mit Radikalkupplungsreaktionen mit TEMPO. Die resultierenden a-(Aminoxy)carbonyl-Verbindungen 2 dienen als wertvolle Vorstufen für 5-endo-oder 5-exo-Cyclisierungsreaktionen.…”

Synthesis of Functionalized Cyclobutane‐Fused Naphthalene Derivatives via Cascade Reactions of Allenynes with tert‐Butyl Nitrite

“…As a result, the formation of 3 a or 4 a was not detected (Scheme 2, reaction 1 and reaction 2), indicating that these reactions follow a radical pathway. Second, the synthesis of 3 a was carried out in the presence of Based on previous reports [8] and our observations, a plausible mechanism accounting for the formation of 3 a from 1 a and 2 is proposed in Scheme 3. Initially, 1 a undergoes [2 + 2] cycloaddition to give intermediate A.…”

“…Therefore, recent studies have focused on finding more sustainable and milder nitrating reagents such as tert-butyl nitrite (TBN), [5] etc. [8] Inspired by those pioneering studies and as a continuation of our own interests in allene derivatives [7c,9] and TBN, [10] we envisioned a synthesis of nitrocyclobutane-fused 2-nitronaphthalen-1-ol (A, Scheme 1). [7] In this regard, Jiang and co-workers have recently disclosed some interesting domino transformations of allenynes.…”

“…[7] In this regard, Jiang and co-workers have recently disclosed some interesting domino transformations of allenynes. [8] Inspired by those pioneering studies and as a continuation of our own interests in allene derivatives [7c,9] and TBN, [10] we envisioned a synthesis of nitrocyclobutane-fused 2-nitronaphthalen-1-ol (A, Scheme 1). This envisioned synthesis is based on a proposed cascade reaction of a benzene-linked allenyne with TBN through the formation of two CÀC bonds and two CÀN bonds as shown in Scheme 1.…”