Four pyrethroids are currently used for crop protection:
permethrin, cypermethrin, decamethrin,
and fenvalerate, compounds obtained by replacing
photolabile centers in earlier esters with alternative
and more stable structural units (Fig. 3). These
pyrethroids are derived from phenoxybenzyl alcohol
first synthesized for other purposes in 1935 or from
a-cyanophenoxybenzyl alcohol known since 1973.
The acid moiety of permethrin was first investigated
by Jihri Farka's in Prague in 1958. He prepared the
allethrin analog with enhanced insecticidal activity
compared to the chrysanthemate. It took 15 years for
this dichlorovinyl acid to appear once again in the
literature, when Elliott showed its importance as a