Annulation

About: Annulation is a research topic. Over the lifetime, 10152 publications have been published within this topic receiving 189701 citations.

Palladium-Catalyzed Annulation of Internal Alkynes by Arene-Containing Vinylic Iodides and Triflates

Abstract: In the presence of a palladium catalyst, internal alkynes undergo carboannulation by cyclic and acyclic vinylic iodides and triflates bearing a neighboring aromatic ring to produce a variety of carbocycles. For example, a number of 9,10-disubstituted-1,2,3,4-tetrahydrophenanthrenes have been prepared in good yields through the palladium-catalyzed annulation of internal alkynes by 2-phenyl-1-cyclohexenyl triflate (1) or 1-iodo-2-phenylcyclohexene (2). This annulation process is fairly general and highly regioselective. The process appears to involve oxidative addition of the vinylic substrate to Pd(0) to produce a vinylic palladium intermediate, which adds the carbon moiety to the less hindered end and the palladium to the more hindered end of the alkyne, followed by intramolecular ring closure onto the neighboring aryl group. The scope and limitations of this methodology are discussed.

Silver-Catalyzed Chemoselective [4+2] Annulation of Two Isocyanides: A General Route to Pyridone-Fused Carbo- and Heterocycles.

Abstract: A silver-catalyzed chemoselective [4+2] annulation of aryl and heteroaryl isocyanides with α-substituted isocyanoacetamides was developed for the facile and efficient synthesis of 2-aminoquinolones, naphthyridines, and phenanthrolines. A mechanism for this multistep domino reaction is proposed on the basis of a 13C-labeling experiment, according to which an unprecedented chemoselective heterodimerization of two different isocyanides generates an α-amidoketenimine intermediate, which undergoes 1,3-amino migration to form an α-imidoylketene, followed by 6 π electrocyclization.

Synthesis of (Carbo)nucleoside Analogues by [3+2] Annulation of Aminocyclopropanes†

Abstract: (Carbo) nucleoside derivatives constitute an important class of pharmaceuticals, yet there are only few convergent methods to access new analogues. Here, we report the first synthesis of thymine-, uracil-, and 5-fluorouracil-substituted diester donor-acceptor cyclopropanes and their use in the indium-and tin-catalyzed [3+2] annulations with aldehydes, ketones, and enol ethers. The obtained diester products could be easily decarboxylated and reduced to the corresponding alcohols. The method gives access to a broad range of new (carbo) nucleoside analogues in only four or five steps and will be highly useful for the synthesis of libraries of bioactive compounds.

Synthesis of (2H)-Indazoles through Rh(III)-Catalyzed Annulation Reaction of Azobenzenes with Sulfoxonium Ylides

Abstract: The rhodium(III)-catalyzed C–H functionalization followed by intramolecular annulation reactions between azobenzenes and sulfoxonium ylides is described. This protocol leads to the efficient formation of 3-acyl (2H)-indazoles with a range of substrate scope. A high level of chemoselectivity and functional group tolerance of this transformation were also observed.