A simple and convenient approach was developed to the selective synthesis of 3‐substituted indoles and benzofurans by the isomerization of 3‐methyleneindoline and benzofuran derivatives catalyzed by Fe(OTf)3. The salient features of this method are the easy availability of substrates, high yield, mild reaction conditions, tolerance of a variety of functional groups, and use of an environmentally friendly catalyst. A possible mechanism has also been proposed for the isomerization process.
A general and efficient synthesis of tetracyclic indolo[2,3-b]quinoline motifs with diverse functional groups is achieved through a simple but conceptually different annulation strategy in excellent yields.
A range of tetracyclic dibenzofuran derivatives bearing a variety of functional groups was readily synthesized via a two-stage domino strategy starting from propargyl ethers of 2-halo phenol derivatives. The first stage in the strategy involves Pd(0)-catalyzed domino intramolecular carbopalladation/Suzuki coupling via 5-exo-dig cyclization onto the alkyne, leading to 3-methylene-2,3-dihydrobenzofuran derivatives. In the second stage of the domino strategy, an iron(III)-catalyzed cycloisomerization and aromatization reaction produces tetracyclic benzofuran derivatives. This two-step sequence provides efficient access to diversely substituted polycyclic dibenzofuran derivatives in high yields and in an atom-efficient and environmentally friendly manner. Moreover, this strategy was also successfully used for the synthesis of a naturally occurring tetracyclic dibenzofuran, β-brazan.
A new and efficient synthesis of tetracyclic phenanthridines and benzo[ c]chromenes has been described involving a metal-mediated two-step domino strategy. The first step involved efficient palladium-catalyzed domino carbopalladation/cross coupling, and the second step involved iron-catalyzed domino isomerization/cyclodehydration. The important features of this strategy include high yields, generality, wide substrate scope, and broad functional group tolerance. A plausible mechanism has been proposed to explain the formation of the product.
A series of diverse and complex hybrid structures of indole bearing fluorene were obtained in the presence of DDQ and FeCl3 with high regioselectivity under mild conditions from biaryl tethered 3-(methylene)indoline in good to excellent yields.
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