Cu(II)-Catalyzed Decarboxylative (4 + 2) Annulation of Coumarin-3-Carboxylic Acids with In Situ Generated α,β-Unsaturated Carbonyl Compounds from -Propargylic Alcohols.

Cu(II)-catalyzed decarboxylative oxidative (4 + 2) annulation of coumarin-3-carboxylic acids with -propargylic alcohols, via the in situ generated α,β-unsaturated carbonyl compounds by the Meyer-Schuster rearrangement, has been developed. This protocol involving indirect C-H functionalization offers access to diverse naphthochromenone architectures with good to excellent yields.

Ru(II)-catalysed oxidative (4 + 2) annulation of chromene and coumarin carboxylic acids with alkynes/propargylic alcohols: isolation of Ru(0) complexes.

Ru(II)-catalysed oxidative (4 + 2) annulation of chromene and coumarin-3-carboxylic acids with alkynes/propargylic alcohols sp C-H bond activation is reported. While the reaction with alkynes affords highly substituted pyrano-chromones in good to excellent yields, the use of methyl-tethered propargylic alcohols in place of alkynes leads to novel Ru(0)-metal complexes in moderate to good yields; these complexes were stable in MeCOH/O. The generality of the reaction with alkynes is illustrated in the case of both symmetrical and unsymmetrical internal alkynes with excellent regioselectivity in the case of unsymmetrical alkynes.

Divergent Reactivity of Phosphorylated and Related Allenes: [4 + 2] Cycloaddition with 3,6-Diphenyltetrazine, Self-Addition Leading to Dimers and [Pd]-Complex Formation.

Phosphorus-based naphthalenes are formed by self-dimerization-cum-cyclization of α-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc)in the presence of PPh and EtN . This reaction involves [4 + 2]-cycloaddition with the (β,γ) double bond of one allene as the dienophile; the double bonds at the α-aryl-(β'') group and (α,-carbons of the second allene act as the diene part. A subsequent proton shift also takes place.

Palladium-Catalyzed Decarboxylative ortho-Amidation of Indole-3-carboxylic Acids with Isothiocyanates Using Carboxyl as a Deciduous Directing Group.

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.

Ruthenium-Catalyzed Oxidative Annulation and Hydroarylation of Chromene-3-carboxamides with Alkynes via Double C-H Functionalization.

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.