Heterocyclization involving benzylic C(sp³)–H functionalization enabled by visible light photoredox catalysis

Abstract

An efficient method for heterocyclization via visible light photoredox catalysis is reported to access various oxygen and nitrogen heterocycles.

Photochemical and Electrochemical Strategies towards Benzylic C−H Functionalization: A Recent Update

“…This represented one of the first examples of benzylic C−H oxidation under photocatalytic conditions. Recently, the same group upgraded the catalytic system enabling the synthesis of both O ‐ and N ‐heterocycles [49] . They employed a ruthenium photocatalyst and Selectfluor for the subsequent oxidation/HAT of the benzylic substrate to form the benzyl carbocation which was trapped intramolecularly by the O ‐ or N ‐nucleophile (Scheme 17).…”

“…In the previous section, we have described Pandey's work on Selectfluor mediated HAT/photoredox benzylic C( sp 3 )−H oxidation (Scheme 17). [49] They have also applied the same strategy for the synthesis of cyclic amines and sulfamidates via C( sp 3 )−H amination (Scheme 20). A variety of electron‐withdrawing substituents on the amine were compatible.…”

“…Recently, the same group upgraded the catalytic system enabling the synthesis of both O-and N-heterocycles. [49] They employed a ruthenium photocatalyst and Selectfluor for the subsequent oxidation/HAT of the benzylic substrate to form the benzyl carbocation which was trapped intramolecularly by the O-or N-nucleophile (Scheme 17). The reaction afforded 5-, 6-and 7membered rings in good yields.…”

Late-stage trifluoromethylthiolation of benzylic C-H bonds

“…As shown in Fig. 1d, the resultant aryl radical cation species 28–36 will lead to inner-sphere HAT with benzylic C–H bonds giving rise to benzylic radicals. Herein, we report the development of a metal-free, photoredox inner-sphere HAT process which predictably generates, from natural products or drug derivatives, a benzylic radical which can be trifluoromethylthiolated, avoiding the use of oxidants and HAT reagents.…”

General Asymmetric Synthetic Strategy for the α‐Alkylated 2,5,6‐Trisubstituted Pyran of Indanomycin and Related Natural Products

“…The resulting alcohol 24 was oxidized with Dess–Martin periodinane to obtain the corresponding aldehyde in 90 % yield. Aldehyde was then subjected to the Grignard reaction with ethylmagnesium bromide to furnish alcohol 25 as a diastereomeric mixture in 86 % yield . Without further purification, the mixture of secondary alcohols 25 was treated with TBAF in THF to afford 26 in 92 % yield .…”