Visible-Light-Initiated Sequential Trifluoromethylation/Remote C(sp³)–H Alkynylation of Vinyl Azides by Radical Relay

Abstract

A visible-light-initiated trifluoromethylation/remote aliphatic C–H alkynylation of α-alkyl-substituted vinyl azides using acetylenic triflones as both the trifluoromethyl and alkyne donors is described. The reaction occurred under environmentally benign and radical initiator-free reaction conditions, affording γ-alkynylated trifluoromethyl ketone derivatives with a broad scope of substituents. Mechanistic studies suggested that the reaction is initiated via a triplet–triplet energy transfer between the 4CzIPN catalyst and acetylenic triflone, followed by fragmentation to generate a trifluoromethyl radical and an alkynyl radical.

Three-Component Photochemical 1,2,5-Trifunctionalizations of Alkenes toward Densely Functionalized Lynchpins

“…Another 1,5-difunctionalization reaction of alkenes via ring opening was developed by Feng, relying on radical attack to 4-isoxazolines with subsequent N–O bond cleavage and radical relocation to the remote position . Furthermore, radical attack to vinyl azides, followed by dinitrogen extrusion and 1,5-HAT of the formed iminyl radical to generate the remote radical was used to 1,5-difunctionalize alkenes . In several methods, the desired 5-position radical is formed via remote CN abstraction after initial radical attack to the alkene, enabling a 1,2,5-trifunctionalization reaction. , Another particularly elegant alkene 1,2,5-trifunctionalization was reported by Han, featuring the migration of an in situ phosphorylated alcohol as the key reaction step …”

“…1,5-Functional group distances are frequently found in organic molecules and prominently present in precursors for the preparation of six-membered heterocyclic systems . Since the simultaneous introduction of both functional groups into simple building blocks constitutes an ideal strategy to access these valuable structures, radical 1,5-difunctionalizations of alkenes have recently attracted increased attention (Figure A). ,− An established approach toward this goal is the addition of a radical to vinylcyclopropanes, followed by opening of the three-membered cycle . Another 1,5-difunctionalization reaction of alkenes via ring opening was developed by Feng, relying on radical attack to 4-isoxazolines with subsequent N–O bond cleavage and radical relocation to the remote position .…”

Visible-light-induced photocatalyst-free activation of alkynyl triflones for trifluoromethylalkynylation of unactivated 1,6-dialkenes

“…Since the initial report of the trifluoromethylalkynylation reaction by Fuchs in 1996, 5 d several elegant trifluoromethylalkynylation reactions have been successfully achieved (Scheme 1a). 6 For example, Zhu's group realized trifluoromethylalkynylation of isocyanides by copper catalysis. 6 a In 2020, Studer's group reported a practical strategy for the site-selective trifunctionalization of terminal alkynes with alkynyl triflones in the presence of AIBN at high reaction temperature.…”