The use of water
in organic synthesis draws attention to its green
chemistry features and its unique ability to unveil unconventional
reactivities. Herein, literature about the use of water as a reaction
medium under visible-light photocatalytic conditions is summarized
in order to highlight challenges and opportunities. Accordingly, this
Synopsis has been divided into four different sections focused on
(1) the unconventional role of water in photocatalytic reactions,
(2) in-/on-water reactions, (3)
water-soluble photocatalysts, and (4) photomicellar catalytic systems.
The possibility to
harness aromatic isocyanides as visible-light
photocatalysts in the α-amino C(sp
3
)–H functionalization
is herein presented. Actually, the three-component cross-dehydrogenative
coupling of aromatic tertiary amines with isocyanides and water leads
to amide products under very mild conditions in high yields and with
a good substrate scope. While the reaction with aromatic isocyanides
proceeds upon direct photoexcitation, aliphatic isocyanides are able
to form a photoactive electron–donor–acceptor complex
with aromatic amines. Moreover, the use of a catalytic loading of
an aromatic isocyanide promotes the oxidative coupling of
N
-phenyl-1,2,3,4-tetrahydroisoquinoline with an array of
different (pro)nucleophiles in good to excellent yields, thus providing
the proof-of-concept for the development of a new highly tunable class
of organic visible-light photocatalysts.
The merging of micellar and photoredox catalysis represents a key issue to promote "in water" photochemical transformations. A photomicellar catalyzed synthesis of amides from N-methyl-N-alkyl aromatic amines and both aliphatic and aromatic isocyanides is herein presented. The mild reaction conditions enabled a wide substrate scope and a good functional groups tolerance, as further shown in the late-stage functionalization of complex bioactive scaffolds. Furthermore, solution 1D and 2D NMR experiments performed, for the first time, in the presence of paramagnetic probes enabled the study of the reaction environment at the atomic level along with the localization of the photocatalyst with respect to the micelles, thus providing experimental data to drive the identification of optimum photocatalyst/surfactant pairing.
The possibility to harness the photoactivity of isocyanides in the development of metal-free Ugi-like visible light photo-triggered multicomponent transformations has been herein reported. More in detail, Ugi-3CR, Ugi-Tetrazole-3CR, and Ugi-...
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