This review describes the characteristic features of simple and nascent N-centered azide radical, and its unique reactivity in fine chemical synthesis with detailed mechanistic discussions.
In this paper, we present fluorescent photoremovable protecting groups (FPRPG) based on bis‐acetyl carbazole for the release of two different functional groups such as carboxylic acids, alcohols, thiols, and amines in a sequential fashion. Dual‐arm caged bis‐acetyl carbazoles with different combinations of two unlike functional groups were synthesized. Photophysical studies showed that caged bis‐acetyl carbazoles are blue fluorescent and their emission properties are sensitive to the environment. Sequential photorelease of two different functional groups by bis‐acetyl carbazole was analyzed by HPLC, UV and emission spectroscopy. The mechanism of the dual release by bis‐acetyl carbazole was investigated and supported by TD‐DFT calculations. To demonstrate the applicability of the dual release ability of bis‐acetyl carbazole FPRPG, we synthesized a drug delivery system (DDS) in which one arm of bis‐acetyl carbazole is linked to the carboxylic functional group of chlorambucil (CBL) and the other arm is attached to the hydroxyl group of ferulic acid ethyl ester (FAEE). In vitro studies showed that our DDS presents excellent properties such as photoregulated dual drug delivery, cellular uptake, and biocompatibility.
This
report presents the oxygenation of C–H bonds via the
merger of photocatalysis and Pd catalysis. Herein, we describe the
utilization of a photocatalyst to oxidize an organopalladium(II) intermediate
to high-valent PdIII or PdIV intermediates,
which promotes the formation of C–O bonds. The demonstrated
method works efficiently with various directing groups, such as oxime
ether and benzothiazole. The applicability of this direct C–O
bond formation method is shown by synthesizing several metal complexes
of 2-(benzo[d]thiazol-2-yl)phenol that can be used
in organic light-emitting diodes and pharmaceuticals.
This report presents the visible‐light‐assisted synthesis of aryl nitriles from easily accessible alcohols or methyl arenes in the presence of O2. Organic photoredox catalyst, 4CzIPN (1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene), induces single electron transfer (SET) from azide N3− and generates azide radical N3⋅.The photogenerated N3⋅ abstracts H atom from α‐C−H bond of benzylic system, which provides aldehyde and hydrazoic acid (HN3) in situ. This reaction subsequently forms azido alcohol intermediate that transforms into nitrile with the assistance of triflic acid (Brønsted acid). A range of alcohols and methyl arenes successfully underwent cyanation at room temperature with good to excellent yields and showed good functional group tolerance.
The combination of an organic photocatalyst [4CzIPN (1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6 dicyanobenzene) or 5MeOCzBN (2,3,4,5,6‐pentakis(3,6‐dimethoxy‐9 H‐carbazol‐9‐yl)benzonitrile)], quinuclidine, and tetra‐n‐butylammonium phosphate (hydrogen‐bonding catalyst) was employed for amide bond formations. The hydrogen‐bonded OH group activated the adjacent C−H bond of alcohols towards hydrogen atom transfer (HAT) by a radical species. The quinuclidinium radical cation, generated through single‐electron oxidation of quinuclidine by the photocatalyst, employed to abstract a hydrogen atom from the α‐C−H bond of alcohols selectively due to a polarity effect‐produced α‐hydroxyalkyl radical, which subsequently converted to the corresponding aldehyde under aerobic conditions. Then the coupling of the aldehyde and an amine formed a hemiaminal intermediate that upon photocatalytic oxidation produced the amide.
Azido radical mediated photocatalytic oxidation method for the selective oxidation of various well‐known feedstocks, such as (hetero)aromatic or aliphatic alcohols, alkylarenes, and terminal alkenes, is successfully accomplished. Herein, the catalytic HAT and reversible addition/elimination strategies of azido radical have been explored to convert the commonly oxidizable functionalities into invaluable carbonyls or tertiary alcohols using an organic photocatalyst 4CzIPN with tetrabutyl ammonium azide (TBAN3) and air/O2 as an oxidant. Indeed, this mild, operationally simple, and productive method offers good to excellent product yields with a wide range of structurally diverse substrates, including pharmaceutical derivatives with good functional group tolerance. Several control experiments have been carried out to investigate the detailed reaction mechanism.
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