Nickel-catalyzed acylzincation of allenes with organozincs and CO

Abstract

Transition metal-catalyzed carbonylative reaction with CO gas are among the central task in organic synthesis, enabling the construction of highly valuable carbonyl compound. Here, we show an earth-abundant nickel-catalyzed three-component tandem acylzincation/cyclization sequence of allene and alkylzinc reagent with 1 atm of CO under mild conditions. This protocol is featured by broad functional group tolerance with high reaction selectivity, providing a rapid and convenient synthetic method for the construction of diverse fully substituted benzotropone derivatives. Mechanistic studies reveal that the installation of a cyano group tethered to allene moiety enables the high regio- and stereoselectivity of this acylzincation of allene, allowing the selective formation of three consecutive C-C bonds in a highly efficient manner.

Dual Photoredox and Nickel Catalysis in Regioselective Diacylation: Exploring the Versatility of Nickel Oxidation States in Allene Activation

“…Concurrently, the synthesis of multifunctional complex molecules has significantly benefited from the migratory insertion process of π-substrates into Ni–C bonds . While migratory insertion steps to Ni-acyl bond frequently involve alkenes, the application of sp -hybridized substrates, specifically alkynes and allenes, remains relatively underexplored (Scheme b). Combining photoredox and Ni catalysis with migratory insertion process, we have conceived a dual catalysis approach for the diacylation of allenes, involving the sequential addition of acyl radicals to Ni­(I) and Ni­(II) intermediates in a Ni­(I)–Ni­(II)–Ni­(II)–Ni­(III)–Ni­(I) catalytic cycle, leading to the formation of 1,4-dione products (Scheme c).…”