Rhodium-catalyzed
oxidative [4 + 2] cyclization reactions through
the C–H activation of azulene carboxylic acids as nonbenzenoid
aromatic compounds with symmetrical and unsymmetrical alkynes were
developed under aerobic conditions, which produced azulenolactone
derivatives with a wide substrate scope and excellent functional group
tolerance. Interestingly, azulenic acids in reaction with alkynes
underwent iridium-catalyzed [2 + 2 + 2] cyclization accompanied by
decarboxylation to afford tetra(aryl)-substituted benzoazulene derivatives.
The reactivity order for C–H activation reaction is greater
toward azulene-6-carboxylic acid, azulene-1-carboxylic acid, and azulene-2-carboxylic
acid. For the first time, the expansion of azulenes having directing
group as nonbenzenoid aromatic compounds for C–H activation
was successful, indicating that nonbenzenoid aromatic compounds can
be used as good substrates for the C–H activation reaction.
Therefore, the research area of C–H activation will certainly
expand to nonbenzenoid aromatic compounds in future.
An efficient, one-pot synthetic method for producing functionalized indolizine derivatives was developed via a Rh-catalyzed [2 + 1]-cyclopropanation, Pd-catalyzed ring expansion, and subsequent oxidation using manganese dioxide from pyridotriazoles and 1,3-dienes.
A rhodium‐catalyzed cyclization reaction of sulfoximines with 3‐diazoindolin‐2‐imines is described. This protocol provides a wide range of indolo‐1,2‐benzothiazines in moderate to excellent yields together with the release of molecular nitrogen and p‐toluenesulfonamide. The present method involves the N–H/C–H activation of S‐aryl sulfoximines and has the advantages of a broad substrate scope.magnified image
Rhodium-catalyzed formal aza-[4 + 3] cycloaddition reaction of 3-diazoindolin-2-imines with 1,3-dienes was demonstrated for the synthesis of azepinoindoles in good to excellent yields in one-pot. First, rhodium-catalyzed [2 + 1] cycloaddition reaction smoothly took place to produce iminyl vinyl cyclopropane intermediate at room temperature in chlorobenzene for 1 h, which was thermally converted to azepinoindoles via aza-Cope rearrangement.
An iridium(III)-catalyzed regioselective acylmethylation of the cage B(4)−H bond in o-carborane acids with sulfoxonium ylides is demonstrated through B(4)−H activation in ethanol under very mild conditions, affording a number of B(4)acylmethylated o-carboranes. Additionally, the selective sequential B(4)-and B(6)-acylmethylation reactions finally gave B(3,5)diacylmethylated o-carboranes in one pot.
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