Chemistry Reference
In-Depth Information
Fig. 2.5
Captan synthesis.
Fig. 2.6
Water-based Diels-Alder
reaction—intermediate to antifungal
compounds.
Fig. 2.7
Claisen rearrangement en
route to cordiachromene.
Fig. 2.
8
A green Michael addition.
in virtually quantitative yield when water was used
as solvent, whereas in organic solvents a highly com-
plex mixture of products was obtained.
Claisen rearrangements are another class of
'waste-free' pericyclic reactions of significant impor-
tance. Claisen rearrangement of the propargyl ether,
which proceeds in 85% yield (Fig. 2.7), is at the
heart of a simple route to cordiachromene [14], a
natural product that shows significant antibacterial
and anti-inflammatory properties.
Addition reactions, in which two molecules
combine to form a single molecule of product, are
another class of inherently waste-free reactions of
widespread applicability. By their very nature, addi-
tion reactions involve an unsaturated bond and are
typified by reactions such as electrophillic addition of
halogens to alkenes and nucleophilic additions to
carbonyls.
Michael additions normally are carried out with
base catalysts, however there have been several
recent examples of very green Michael additions
that occur in high yield in water. A striking example
of this is the addition of acrolein to 2-methyl-1,
3-cyclopentadione [15], which proceeds in quantita-
tive yield in water at ambient temperature (Fig.
2.8).
