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Title
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Silica-bonded 5-n-propyl-octahydro-pyrimido[1,2-a]azepinium chloride (SB-DBU)Cl as a highly efcient, heterogeneous and recyclable silica-supported ionic liquid catalyst for the synthesis of benzo[b]pyran, bis(benzo[b]pyran) and spiro-pyran derivatives
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Abstract
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The reaction of 3-chloropropyl silica (SilprCl) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in dry
acetone affords silica-bonded 5-n-propyl-octahydro-pyrimido[1,2-a]azepinium chloride (SB-DBU)Cl as
a new silica-supported ionic liquid catalyst. Afterward, (SB-DBU)Cl is used for the ef?cient synthesis
of 4H-benzo[b]pyran derivatives via the one-pot, three-component reaction of carbonyl compounds
(cyclohexane-1,3-dione, 5,5-dimethylcyclohexane-1,3-dione or 3-methyl-1-phenyl-2-pyrazolin-5-one)
with aromatic aldehydes and alkylmalonates. Moreover, some novel bis(benzo[b]pyran)s and a broad
range of structurally diverse spiro-pyrans containing oxindole and/or quinoxaline moiety in their structures
are synthesized using (SB-DBU)Cl. The catalyst is recycled and reused ?fteen times with unchanged
yield.
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