In order to evaluate the practicality of the given method, a gram-scale synthesis was performed to afford the product
3a in 73% yield under the standard conditions (
Scheme 4a). The access to molecular diversity was demonstrated by the post-functionalizations of generated pyrrole products
3a and
5a, as shown in
Scheme 4. Multiple transformations of substituents on
3a could proceed smoothly and various functional group including primary amine, formyl, alkynyl, iodo and amide were introduced successfully (
Scheme 4a). These functionalized pyrroles were not easily accessible through usual approach and will find potential applications for further deliberation, generating advanced organic building blocks. Among which, the isolation of product
6 could be achieved by the cleavage of
N-sulfonamide group of
3a in the presence of Ti(O
iPr)
4, TMSCl and Mg powder. Alternatively, the primary amine
6 could be afforded in quantitative yield through the deprotection of
N-phthalimidyl group of pyrrole
3r in the presence of hydrazine hydrate. The
N–
tert–butyl substituent was removed smoothly with the assistance of hydrochloric acid, affording product
7 in almost quantitative yield. Besides, the selective conversion of cyano group of
3a could be realized under different conditions, providing 2-formyl pyrrole
8 and 2-carboxamidyl pyrrole
9 in good yields, respectively. The iodo group was introduced into
3a smoothly by reacting with
N-iodosuccinimide and gave a fully substituted pyrrole
10, which was subsequently reacted with trimethylsilylacetylene through the Sonogashira coupling. Followed by the removal of trimethylsilyl (TMS) group, the product
12 with a terminal alkynyl group was afforded successfully. In addition, through the introduction of bromo group and Suzuki coupling with phenylboronic acid,
5a was transformed into a 4, 5-diphenylpyrrole
14 in 50% yield (
Scheme 4b), which was the key precursor of bifunctional antitumor agents [
50]. Notably, after the removal of
N–
tert–butyl group of
5a in the presence of TfOH, compound
15 was successfully ammoniated with the utilization of
O-(2, 4-dinitrophenyl)hydroxylamine and NaH [
51], and then cyclized with formamidine acetate to produce pyrrolo[2, 1-
f][1, 2, 4]triazine
17 in 79% yield [
52], which is the analogue of the nucleobase of Remdesivir, one of the most promising anti-COVID-19 medicines at present. Besides, with the promotion of [Cp*RhCl
2]
2 and Cu(OAc)
2, the cyclization of compound
15 could occur successfully with ethyl acrylate, leading to the formation of 5
H-pyrrolo[2, 1-
a]isoindole
18 in 83% isolated yield (
Scheme 4b) [
53]. All of the above transformations demonstrated that this protocol possessed extraordinary reactivity towards various regents, allowing the efficient assembly of diverse pyrrole derivatives and further application in multiple fronts.