Chloroformylation reactions are versatile
reactions that allow
the introduction of a chlorine atom and an aldehyde group in enolizable
ketones, employing the well-known Vilsmeier reagent. However, the
use of this unstable reagent is usually associated with hazards, especially
when it is used on an industrial scale. The present article describes
the preparation and use of the Vilsmeier reagent under continuous
flow conditions for the preparation of an important intermediate in
the synthesis of cyanine dyes. In addition, the traditionally used
dimethylformamide has been substituted with more desirable formamides,
together with the removal of the halogenated solvent usually employed
in the reaction. Consequently, the optimized conditions allow the
continuous production of the target compound in a 79–81% isolated
yield in a more environmentally friendly, fast, and secure manner.
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