Abstract
We have developed an efficient annulation of benzamides with allenes using cobalt and photoredox dual catalysis under an oxygen atmosphere. The transformation features an alternative strategy for the regeneration of a cobalt catalyst with the aid of Eosin Y.
Highlights
Transition-metal-catalyzed direct C − H functionalizations have emerged as efficient, powerful, and straightforward approaches for the construction of carbon-carbon and carbon-heteroatom bonds over the past few decades [1,2,3,4,5,6]
Preliminary mechanism studies reveal that a radical-mediated cascade annulation is involved in this reaction
A slight increase in the amount of cobalt made significant effect in promoting the reaction, and the excellent yield was obtained when the annulation reaction was performed with 20 mmol% Co(acac)2 under the similar reaction conditions
Summary
Transition-metal-catalyzed direct C − H functionalizations have emerged as efficient, powerful, and straightforward approaches for the construction of carbon-carbon and carbon-heteroatom bonds over the past few decades [1,2,3,4,5,6]. Among the first-row transition metals, the unique properties of cobalt in varied oxidation states have witnessed the powerful ability to manipulate various chemical bonds as a result of the chelation-assisted direct metalation of azobenzene [11,12,13,14,15,16]. Among such elegant transformations, a number of C − H activation and oxidative annulation reactions with various unsaturated coupling partners, such as alkynes and alkenes, have garnered considerable attention for molecule diversity in step- and atom- economical strategies [17]. Ackermann group disclosed an electrochemical C − H activation with allenes which enabled the high valent cobalt regeneration under the anodic oxidation (Scheme 1a) [62,63]
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