Recently the aqueous medium has attracted the interest of organic chemists,
and many, sometimes surprising, discoveries have been made. Among the orga
nic reactions investigated in aqueous medium, the Diels-Alder cycloaddition
has been the most widely studied because of its great importance in the sy
nthetic and theoretical fields. The Diels-Alder reaction is greatly enhance
d by Lewis acid catalysis, and this review illustrates recent significant r
esults in this field when the reaction is performed in aqueous medium.