The Biginelli reaction has been reviewed.5 Several
improved protocols for the preparation of DHPMs have
recently been reported, either by modification of the
classical one-pot condensation approach itself,6–10 or by
the development of novel, but more complex, multi-step
strategies.11 However, some of the newer reported methods
also suffer from drawbacks such as unsatisfactory
yields, cumbersome product isolation procedures and
environmental pollution.6,12–17 Moreover some of the
methods are only practical for aromatic aldehydes.
6,11d,15,17 Therefore, a need still exists for versatile,
simple and environmentally friendly processes whereby
DHPMs may be formed under milder and practical
conditions.