Our recent studies concerning to the ozonolysis of various azoles are
reviewed in this paper. While azoles are remarkably stable under the-a
cidic, basic, oxidative and/or reductive conditions due to their aroma
tic characters, azoles are specifically labile toward ozone. These cha
racters of azoles satisfy the requirement for the protection-deprotect
ion of the functional group. Pyrroles are easily prepared from primary
amines, and the side chains of these pyrroles are functionalized by b
ase catalyzed alkylation, hydride reduction, and aminolysis. By the oz
onolysis, pyrroles are converted into the corresponding amides. Throug
h this series of the reactions, pyrroles are demonstrated to be useful
as the protecting group of amino functions for the synthesis of alpha
-aminoalcohols, alpha-aminoketones, alpha-aminoaldehydes, and some pep
tides. Oxazole ring is also useful as the protecting group of carboxyl
group in peptide synthesis, and the ring opening is carried out by oz
onolysis. In this deprotection, oxazoles are converted into acid anhyd
rides, which are the reactive forms of carboxyl. group and are directl
y available for the further peptide formation. This is the most remark
able example that the protecting group takes a role of the precursor o
f the active form of the functional group.