The alkylation and heteroarylation of unactivated tertiary, secondary, and primary C­(sp3)–H bonds was achieved by employing an acridinium photoredox catalyst along with readily available pyridine N-oxides as hydrogen atom transfer (HAT) precursors under visible light. Oxygen-centered radicals, generated by single-electron oxidation of the N-oxides, are the proposed key intermediates whose reactivity can be easily modified by structural adjustments. A broad range of aliphatic C–H substrates with electron-donating or -withdrawing groups as well as various olefinic radical acceptors and heteroarenes were well tolerated.

The synthesis of all-carbon-substituted, quaternary stereocenters through Lewis acid-catalyzed Friedel-Crafts alkylation of cyclic and acyclic 2-hydroxy oxime ethers proceeds under mild reaction conditions and with high yields. Moreover, the oxime ether moiety can be easily manipulated into various functional groups through subsequent modifications.

The rapid assembly of molecular complexity continues to be at the forefront of novel reaction development. In the pursuit of that goal, we herein report a novel Sc(OTf) -catalyzed, one-pot multicomponent reaction that furnishes complex multicyclic 2-pyrrolines with excellent overall yields and perfect diastereocontrol. This process is based on our previously established (2+2+1)-cycloannulation of in situ generated 1-azaallyl cations, 1,3-dicarbonyls and primary amines. The newly formed and highly reactive aminal moiety is readily substituted with indoles and pyrroles both as external and internal π-nucleophiles to provide densely functionalized N-heterocycles with four new σ-bonds and two vicinal quaternary stereogenic centers. In addition, DFT calculations have been conducted to further characterize the intermediate 1-azaallyl cations.

The first Sc(OTf)-catalyzed dehydration of 2-hydroxy oxime ethers to generate benzylic stabilized 1-azaallyl cations, which are captured by 1,3-carbonyls, is described. A subsequent addition of primary amines in a sequential three-component reaction affords highly substituted and densely functionalized tetrahydroindeno[2,1- b]pyrroles as single diastereomers with up to quantitative yield. Thus, three new σ-bonds and two vicinal quaternary stereogenic centers are generated in a one-pot operation.