Executing photoredox
reactions in flow offers solutions to frequently
encountered issues regarding reproducibility, reaction time, and scale-up.
Here, we report the transfer of a photoredox-catalyzed benzylic coupling
of alkylarenes to aldehydes to a flow chemistry setting leading to
improvements in terms of higher concentration, shorter residence times,
better yields, ease of catalyst preparation, and enhanced substrate
scope. Its applicability has been demonstrated by a multi-gram-scale
reaction using high-power light-emitting diodes (LEDs), late-stage
functionalization of selected active pharmaceutical ingredients (APIs),
and also a photocatalyst recycling method.
N
-heterospirocycles are interesting
structural
units found in both natural products and medicinal compounds but have
relatively few reliable methods for their synthesis. Here, we enlist
the photocatalytic generation of
N
-centered radicals
to construct β-spirocyclic pyrrolidines from
N
-allylsulfonamides and alkenes. A variety of β-spirocyclic
pyrrolidines have been constructed, including drug derivatives, in
moderate to very good yields. Further derivatization of the products
has also been demonstrated as has a viable scale-up procedure, making
use of flow chemistry techniques.
The nitrosation of several alkanes using tert-butyl nitrite has been performed in flow showing a remarkable reduction in the reaction time compared with batch processing. Due to the necessity for large excesses of the alkane component a continuous recycling process was devised for the preparation of larger quantities of material.
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