Visible Light-Induced Radical Cyclization of Tertiary Bromides with Isonitriles To Construct Trifluoromethylated Quaternary Carbon Center

Bromide-promoted cascade annulation of isocyanobiaryls with aldehydes through photoredox catalysis

Herein, we report a cascade annulation of readily available isocyanobiaryls with simple aldehydes via photoredox catalysis, providing a straightforward approach towards valuable 6-hydroxyalkylated phenanthridines. Mechanistic studies indicated the generation of a key acyl radical from aldehydes by hydrogen atom abstraction with a bromine radical. This protocol exhibits exceptional chemoselectivity, excellent tolerance of various functional groups and mild reaction conditions. Its synthetic utility was demonstrated by a gram-scale reaction and various facile manipulations of the free hydroxyl group to furnish diverse phenanthridine derivatives.

α-Halocarbonyls as a Valuable Functionalized Tertiary Alkyl Source

This review introduces the synthetic organic chemical value of α-bromocarbonyl compounds with tertiary carbons. This α-bromocarbonyl compound with a tertiary carbon has been used primarily only as a radical initiator in atom transfer radical polymerization (ATRP) reactions. However, with the recent development of photo-radical reactions (around 2010), research on the use of α-bromocarbonyl compounds as tertiary alkyl radical precursors became popular (around 2012). As more examples were reported, α-bromocarbonyl compounds were studied not only as radicals but also for their applications in organometallic and ionic reactions. That is, α-bromocarbonyl compounds act as nucleophiles as well as electrophiles. The carbonyl group of α-bromocarbonyl compounds is also attractive because it allows the skeleton to be converted after the reaction, and it is being applied to total synthesis. In our survey until 2022, α-bromocarbonyl compounds can be used to perform a full range of reactions necessary for organic synthesis, including multi-component reactions, cross-coupling, substitution, cyclization, rearrangement, stereospecific reactions, asymmetric reactions. α-Bromocarbonyl compounds have created a new trend in tertiary alkylation, which until then had limited reaction patterns in organic synthesis. This review focuses on how α-bromocarbonyl compounds can be used in synthetic organic chemistry.

Redox-Neutral Cyclization of 2-Isocyanobiaryls through Photoredox/PPh3 Dual Catalysis

The photoredox/PPh3-mediated cyclization of 2-isocyanobiaryls has been developed. A substantial range of functional-group-rich phenanthridine derivatives were synthesized at room temperature in a highly selective and atom-economic manner. Mechanistic studies suggested that the cyclization process is probably mediated both by Ph3P radical cation with key 1,2-hydride transfer and hydrogen atom generated through O-H bond homolytic cleavage of Ph3P-OH radical intermediate.

Synthesis of α-Hydroxyl and α-Amino Pyridinyl Esters via Photoreductive Dual Radical Cross-Coupling

A method for the synthesis of α-hydroxyl and α-amino pyridinyl esters via photoreductive dual radical cross-coupling catalyzed by the super-organoreductant CBZ6 has been developed. A wide range of 2-pyridinylation and 4-pyridinylation of either α-ketoesters or imine derivatives has been achieved. The applications in the synthesis of pyridinyl amino-hydroxyl acids as well as a new chiral oxazoline ligand have also been accomplished.

Hantzsch Ester-Mediated Synthesis of Phenanthridines under Visible-Light Irradiation

An efficient photocatalytic synthesis of phenanthridines mediated by an organo-photoredox initiator Hantzsch ester has been developed via denitrogenative intramolecular annulation of benzotriazolyl chalcones. The highly reducing photoactivated Hantzsch ester facilitates the transformation of benzotriazolyl chalcones into phenanthridinyl chalcones through photoinduced electron transfer (PET) and hydrogen atom transfer (HAT) processes. The mild reaction conditions utilizing inexpensive Hantzsch ester as photosensitizer, wide reaction scope and excellent functional group tolerance are notable attributes of the methodology.

Construction of trifluoromethylated quaternary stereocenters via p-quinone methides

Development of a new synthetic method for the construction of quaternary centers with a CF₃ group was realized by way of 1,6-addition of various nucleophiles to highly reactive δ-trifluoromethylated p-quinone methides generated in situ.

Syntheses of α-CF3-α-quaternary ketones via p-quinone methides and their derivatization to compounds with successively congested stereogenic centers

NHC-catalyzed 1,6-conjugate additions of a variety of aldehydes to δ-CF₃-δ-substituted p-quinone methides and their highly diastereoselective derivatization to compounds with successively congested stereogenic centers were performed.