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Chapter 4
Synthesis of highly substituted pyrazolopyrimidine
one broad singlet at δ = 5.57 ppm assigned to –NH 2 groups, one singlet at δ = 7.28
ppm assigned to –CONH groups and one broad singlet observed at δ = 11.9 ppm
assigned to pyrazole -NH.
The structures of 9a-x were established on the basis of their elemental analysis
and spectral data (MS, IR, and 1 H NMR). The analytical data for 9i revealed a
molecular formula C 16 H 21 NO 2 S 2 (m/z 323). The 1 H NMR spectrum revealed a singlet
at δ = 1.18-1.20 ppm assigned to isopropyl-CH 3 , a singlet at δ = 1.57 ppm assigned to
the –CH 3 protons, a singlet at δ = 2.44 ppm assigned to (2 × SCH 3 ) , a multiplet at δ =
3.17-3.24 ppm assigned to the isopropyl -CH protons, a multiplets at δ = 6.99–7.54
ppm assigned to the aromatic protons, and one broad singlet at δ = 8.38 ppm assigned
to -CONH groups.
The structures of 10a-x were established on the basis of their elemental
analysis and spectral data (MS, IR, 1 H NMR and 13 C NMR). The analytical data for
10b revealed a molecular formula C 23 H 26 ClN 5 O 2 S 2 (m/z 503). The 1 H NMR spectrum
revealed a multiplets at δ = 1.35-1.81 assigned to 10 protons of (5x CH 2 ) groups in
cyclohexane ring, a singlet at δ = 2.45 ppm assigned to - SCH 3, a singlet at δ = 2.70
ppm assigned to - CH 3, a multiplet at δ = 3.79 ppm assigned to the –CH protons of
cyclohexane ring, a multiplet at δ = 7.05–8.00 ppm assigned to the aromatic protons,
one singlet at δ = 8.56 ppm assigned to –CONH groups attached with cyclohexane
ring, and one singlet observed at δ = 12.56 ppm assigned to –CONH group attached
with phenyl ring.
The proposed mechanism for the cyclization is shown in Figure-24. The
endocyclic-NH in compound A is the most nucleophilic center it is also the most
sterically hindered site. Therefore, addition takes place at the exocyclic-NH 2 groups.
The nucleophilic amino group attacks on the double bond via a Michael addition
reaction, followed by loss of the thiomethane group. The intermediate D then cyclizes
with subsequent dehydration E to afford the pyrazolopyrimidine derivative F.
Department of Chemistry, Saurashtra university, Rajkot-360005 136