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Chapter – 5 Synthesis and Characterization…..
5.5 AIM OF CURRENT WORK
Our group is involved in the synthesis of aryl amino coumarins since
last few years, where, aryl amino coumarins showed good antitubercular
activity. Previously, preparation of differently substituted aryl amino coumarins
was only the aim. Afterwards, the aryl amino coumarins were further cyclized
to give fused pyridine as well as fused benzothiazine derivatives, which
showed good antitubercular as well as anticancer activity. Looking to the
interesting biological profile showed by coumarin benzothiazine derivatives
and their unexplored chemistry part and from the literature survey, it was
decided to modify previously prepared fused benzothiazines derived from aryl
amino coumarins into N-substituted benzothiazine derivatives so that Nalkylation
was carried out on coumarin benzothiazine derivatives by different
methods but it failed. Then N-alkylation was carried out on aryl amino
coumarin derivatives but it also failed. Afterwards, new route was thought by
which benzothiazine derivatives could be synthesized that is why the Mannich
reaction was carried out on aryl amino coumarins in order to prepare N-
Mannich bases of aryl amino coumarins and their further cyclization into
benzothiazine derivatives. But to our surprise, the Mannich reaction on aryl
amino coumarin resulted into unusual new product formation which has been
discussed in results and discussion in detail.
Literature revealed that Mannich reaction is not reported on aryl amino
coumarins but similar kind of scaffold is reported 60 . Where Mannich reaction
was carried out on 4-hydroxy coumarin and the hydroxyl group present at 4 th
position in coumarin nucleus was converted into chloro which was easily
removed by the treatment of aromatic primary amine. As discussed in chapter
– 1, Mannich bases can be synthesized by Mannich reaction on nitrogen of
secondary amine by using simplified methodology and easy work up and this
inspired us to develop some new aryl amino coumarin derivatives by Mannich
reaction for our targeted work. Formaldehyde solution (37-41 %) and different
type of secondary amines were used to acquire Mannich bases under acidic
Department of Chemistry, Saurashtra University, Rajkot – 360 005 290