Intermolecular tandem copper-catalyzed O-arylation-oxidative acylation (cross dehydrogenative coupling-CDC) has been developed under air as an oxidant. The reaction between 2,4-dihydro-3H-pyrazol-3-ones and ortho-halo aryl carboxaldehydes furnished the corresponding chromone fused pyrazoles, in a straightforward manner. The synthetic utility of the presented tandem catalysis has been demonstrated with the synthesis of an A-subtype selective adenosine receptor antagonist in only two steps.
A unique
intramolecular vinylogous Michael addition leading to
the synthesis of heterocycles has been disclosed. Base-promoted one-pot
sequential O-allylation of o-hydroxy-cinnamates
or -cinnamonitrile or -chalcones with γ-bromocrotonates followed
by an intramolecular conjugate addition of vinylogous Michael donors
resulted in the formation of highly substituted benzofuran derivatives
in good to excellent yields. The intramolecular event followed by
two [1,3]-H shifts leading to aromatization appears to be the key
to the success of this unprecedented transformation.
A base-mediated tandem aza-Michael addition-vinylogous nitroaldol condensation has been described between 3,5-dialkyl 4-nitropyrazoles and alkynyl ketones/aldehydes. This transition metal-free atom economical transformation occurred via C-N and C═C bond formations in one step with the elimination of water. The construction of a variety of highly substituted N-fused 3-nitropyrazolopyridine derivatives has been demonstrated with good yields. Good to excellent regioselectivities have been achieved with unsymmetrically substituted 4-nitropyrazoles.
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