Ruthenium-catalyzed oxidative annulation of 2H-chromene-3-carboxamides with alkynes has been achieved by using the directing group nature of amide in the presence of Cu(OAc)·HO as an oxidant and AgNTf as an additive. This reaction offers a broad substrate scope, and both symmetrical and unsymmetrical alkynes can be harnessed. High regioselectivity was achieved in the case of unsymmetrical alkynes. In addition, we have also accomplished double C-H activation by employing an excess of alkyne, where both annulation and hydroarylation took place regio- and stereoselectively in one pot, with the catalyst playing a dual role. While the first C-H functionalization could involve Ru-N covalent bond, the second C-H functionalization most likely involves Ru-O coordinate bond. The structures of key products are confirmed by X-ray crystallography.
Owing to the utmost importance of anthracene based phosphonates in multiple branches of science, we offer a direct, metal‐free and operationally‐simple protocol to access a new family of anthracenylphosphonates, i. e., diethyl ((10‐arylanthracen‐9‐yl)methyl)phosphonates by Friedel‐Crafts (FC) type arylation reactions of easily accessible corresponding α‐hydroxyphosphonate with arenes (1.2 equiv only) in the presence of inexpensive acid. The scope has been extended with both activated and unactivated arenes including haloanisoles, heteroarenes and biphenyl at room temperature. Unexpectedly, under identical reaction conditions, pyrene afforded the α‐pyrene substituted anthracenylphosphonates. Furthermore, these anthracenyl along with recently reported naphthyl phosphonates were screened for their activities against murine melanoma cell lines (skin cancer). Initial studies exhibited promising results with the IC50 values in the range of 9.46‐96 μm for anthracenylphosphonates and 15–38 μm for naphthylphosphonates.
Palladium-catalyzed ortho-amidation of indole-3-carboxylic acids with isothiocyanates by using the deciduous directing group nature of carboxyl functionality to afford indole-2-amides is demonstrated. Both C-H functionalization and decarboxylation took place in one pot, and hence, this carboxyl group served as a unique, deciduous (or traceless) directing group. This reaction offers a broad substrate scope as demonstrated for several other heterocyclic carboxylic acids like chromene-3-carboxylic acid, imidazo[1,2- a]pyridine-2-carboxylic acid, benzofuran-2-carboxylic acid, pyrrole-2-carboxylic acid, and thiophene-2-carboxylic acid. In the reaction using 2-naphthoic acid, of the two possible isomers, only one isomer of the amide was exclusively formed. The indole-2-amide product underwent palladium-catalyzed C-H functionalization to afford the diindole-fused 2-pyridones by combining two molecules of the indole moiety, with the elimination of an amide group from one of them, attached at the C3-position for the C-C/C-N bond formation. The structures of key products are confirmed by X-ray crystallography.
The divergent behaviour of 3-alkynylindole-2-carboxamides, under palladium catalysed conditions and phase-transfer catalytic conditions, is described. Thus, palladium catalysed intramolecular C-N and C-C bond formation in a single step by C-H activation involving 3-alkynylindole-2-carboxamides and leading to pyrrolodiindolones in high yields is developed. In contrast, using the same precursors, a high yielding regio- and chemo-selective route for 3-substituted β-carbolinones by phase-transfer catalysis is established via intramolecular C-N bond formation. The structures of key products are confirmed by X-ray crystallography.
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