We have developed a metal-free, mild,
and green synthetic route
toward benzothieno[3,2-b]benzofurans by the annulation
of 3-nitrobenzothiophene with phenols. The reaction was found to be
general with a range of substituted phenols. In addition, we could
extend the methodology for the synthesis of pentacenes and could demonstrate
the synthesis in gram-scale. Moreover, we extended the strategy for
the synthesis of benzothieno[2,3-b]benzofurans by
starting from 2-nitrobenzothiophenes.
An NHC-mediated synthesis of pyrrolo[2,1-a]isoquinoline and indolizine derivatives with potential biological activity is reported (NHC=N-heterocyclic carbene). The preliminary photophysical studies of such compounds reveal that they have potential application in the sensing of volatile organic compounds (VOCs).
Although NHC-catalyzed
umpolung of imines are known, the related
reactions under oxidative conditions are limited. Described herein
is the two-step process involving the initial formation of aldimines
from the corresponding aldehydes and 2-amino benzyl alcohols followed
by NHC-catalyzed cyclization proceeding via the imidoyl azoliums under
oxidative conditions. The reaction allowed the synthesis of trifluoromethylated
3,1-benzoxazines in good yields and broad scope. The role of NHC in
the intramolecular cyclization and preliminary mechanistic experiments
are also provided.
A nucleophilic heterocyclic carbene mediated homoenolate annulation of enals to aurone analogs leading to the efficient synthesis of cyclopentene-fused spirobenzofuran-3-ones is reported.
An unprecedented three component reaction involving arylidene oxazolone, enal and NHC, leading to the synthesis of fully substituted cyclopentanone derivatives with three contiguous stereocenters, is reported.
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