Cost-Effective Carbon Quaternization with Redox-Active Esters and Olefins.

Quaternary carbons are embedded in various natural products, pharmaceuticals, and organic materials; however, constructing this valuable motif is far from trivial. Conventional approaches mainly rely on classical polar disconnections and encounter bottlenecks concerning harsh conditions, functional group tolerance, regioselectivity, and step economy. In this context, Kawamata, Baran, Shenvi, and coworkers recently demonstrated that two feedstock chemicals, alkyl carboxylic acids and olefins, could be utilized to construct tetrasubstituted carbons in the presence of an inexpensive iron porphyrin catalyst and a suitable reductant combination through quaternization of radical intermediates. The method enabled access to various sterically encumbered quaternary carbons under mild and robust conditions. Taking a complete detour from conventional approaches, the present heteroselective radical-radical coupling simplifies the synthesis of quaternary carbon-containing molecules through an innovative and distinctive disconnection approach.

Direct C-H alkylation of 3,4-dihydroquinoxaline-2-ones with N-(acyloxy)phthalimides via radical-radical cross coupling.

We present an organophotoredox-catalyzed direct Csp3-H alkylation of 3,4-dihydroquinoxalin-2-ones employing N-(acyloxy)pthalimides to provide corresponding products in good yields. A broad spectrum of NHPI esters (1°, 2°, 3°, and sterically encumbered) participates in the photoinduced alkylation of a variety of 3,4-dihydroquinoxalin-2-ones. In general, mild conditions, broad scope with good functional group tolerance, and scalability are the salient features of this direct alkylation process.

Photodecarboxylative Radical Cascade Involving N-(Acyloxy)phthalimides for the Synthesis of Pyrazolones.

We disclose N'-arylidene-N-acryloyltosylhydrazides as novel skeletons for the synthesis of biologically relevant alkylated pyrazolones through a photoinduced radical cascade with N-(acyloxy)pthalimides as readily available alkyl surrogates. The reaction proceeds through the formation of a photoactivated electron donor-acceptor (EDA) complex between alkyl N-(acyloxy)phthalimide (NHPI) esters and LiI/PPh3 as a commercially available donor system. The reaction exhibits a broad scope and scalability, thereby enabling synthesis of a broad spectrum of functionally orchestrated alkylated pyrazolones under mild and transition-metal-free conditions.