reactive functionalities such as the sulfonyl chlorides under standard basic conditions. A one-pot
synthesis of the monomethoxytritylated aminobenzotriazole was also attempted and gave a 46 % yield
compared to the three-step procedure which gave a 33 % yield. Both routes required one column
chromatography purification.
The base stability of the triazole-protected species (4) and (5) was examined to determine the extent of
basic conditions permissible for further reaction. The following bases were used: concentrated ammonia,
piperidine, DBU and sodium methoxide. Both compounds (4) and (5) were stable at room temperature
for 24 h to all of the bases, however, when heated the monomethoxytritylated aminobenzotriazole was
converted back to 5-aminobenzotriazole after 30 min by all of the bases. In contrast the benzylated
aminobenzotriazole (5) was stable when heated with all of the bases. In addition to using acid labile
protecting groups two base labile protecting groups were examined on the triazole ring. The pivaloyl and
fluorenylmethyl groups were added to the trifluoroacetamide protected aminobenzotriazole (1) and their
stability to potassium carbonate and heat tested. Both the hindered amide and carbamate were cleaved by
heating in potassium carbonate indicating their unsuitability as protecting groups for aminobenzotriazole.
Thus, the acid labile groups were chosen for further reactions.
The conditions for removal of the monomethoxytrityl and benzyl groups were investigated and it was
found that TFA cleaved both protecting groups cleanly in 15 min to return the aminobenzotriazole. In the
case of the monomethoxytrityl an excess of pyrrole was also added as a scavenger,7. to trap the tertiary
cation formed which can react with the liberated amine again.
In order to demonstrate the usefulness of these compounds the monomethoxytritylated
aminobenzotriazole was coupled to rhodamine B sulfonyl chloride and dansyl chloride in pyridine with a
catalytic amount of DMAP in a repetition of the previous experiments with the unprotected 5-
aminobenzotriazole. (Scheme 2) The rhodamine derivative (6) was isolated by column chromatography in
88 % yield before removal of the monomethoxytrityl group using TFA and pyrrole gave the desired
compound (7) in 89 % after purification by chromatography. The reaction with dansyl chloride gave the
protected species (8) in 64 % yield after a basic extraction and the desired compound (9) was produced
after removal of the protecting group.
In conclusion, this communication demonstrates how to selectively protect 5-aminobenzotriazole to
ensure a clean reaction at the primary amine group. The protecting groups have been chosen for use
under basic conditions which favour the types of reaction normally used with primary amines. Two
fluorescent compounds that had been difficult to synthesis previously from 5-aminobenzotriazole were
prepared in good yield. The use of these protected benzotriazole compounds will allow the synthesis of a
range of compounds for use in the study of metal ions or metal surfaces.