4 research outputs found
Molybdenum-Catalyzed Synthesis of Nitrogenated Polyheterocycles from Nitroarenes and Glycols with Reuse of Waste Reduction Byproduct
A novel domino reduction/imine formation/intramolecular
cyclization/oxidation
for the efficient synthesis of pyrrolo(indolo)[1,2-<i>a</i>]quinoxalines and pyrrolo(indolo)[3,2-<i>c</i>]-quinolines
from readily available nitrobenzenes and glycols is reported. The
process utilizes the carbonyl byproduct of the initial dioxomolybdenum(VI)-catalyzed
reduction of nitroaromatics with glycols as a reagent for the imine
generation. This method represents the first sustainable domino reaction
for the preparation of biologically relevant heterocycles that internally
incorporates the waste formed in the first step to the final product
Formal [4 + 1] Cycloadditions of β,β-Diaryl-Substituted <i>ortho</i>-(Alkynyl)styrenes through Gold(I)-Catalyzed Cycloisomerization Reactions
Gold(I)-catalyzed cycloisomerization
of β,β-diaryl-<i>o</i>-(alkynyl)styrenes at
80 °C selectively yields dihydroindeno[2,1-<i>a</i>]indenes in a transformation that encompasses a formal
[4 + 1] cycloaddition and takes place through a cascade 5-<i>endo</i>-cyclization–diene activation–<i>iso</i>-Nazarov cyclization. In addition, by performing the
reaction at 0 °C, the same substrates exclusively give rise to
benzofulvene derivatives, which have also been shown to be intermediates
in the formation of the tetracyclics
Straightforward Synthesis of Dihydrobenzo[<i>a</i>]fluorenes through Au(I)-Catalyzed Formal [3 + 3] Cycloadditions
Dihydrobenzo[<i>a</i>]fluorene derivatives have been prepared by a formal intramolecular [3 + 3] cycloaddition of <i>o</i>-alkynylstyrenes bearing a secondary alkyl group at the β-position of the styrene moiety. The process, catalyzed by a cationic gold(I) complex, involves a 1,2-hydride migration as the key step. 6,11-Dihydro-5<i>H</i>-benzo[<i>a</i>]fluorenes could be obtained from the initially generated 6,6a-dihydro-5<i>H</i>-benzo[<i>a</i>]fluorenes by subsequent heating of the reaction mixture under gold(I) or Brønsted acid catalysis or directly by conducting the reactions at high temperature
Synthesis of Functionalized 1<i>H</i>‑Indenes and Benzofulvenes through Iodocyclization of <i>o</i>‑(Alkynyl)styrenes
A convenient
method for the preparation of synthetically useful
3-iodoindene derivatives has been developed. This protocol, based
on the 5-endo iodocyclization reaction of <i>o</i>-(alkynyl)styrenes,
represents one of the scarce examples of halocyclizations using olefins
as nucleophilic counterparts and allows the synthesis of both 3-iodo-1<i>H</i>-indenes (from β-alkyl-β-alkyl/aryl-<i>o</i>-(alkynyl)styrenes) and 3-iodobenzofulvenes (from β,β-diaryl-<i>o</i>-(alkynyl)styrenes) in good yields under mild reaction
conditions. In addition, related alkoxyiodocyclization processes are
described, which are particularly interesting in their intramolecular
version because they allow the synthesis of heteropolycyclic structures
containing the indene core. Finally, the usefulness of the prepared
3-iodoindenes has been demonstrated by the synthesis of several polysubstituted
indene derivatives through conventional palladium-catalyzed cross-coupling
reactions and iodine–lithium exchange processes