Pd/phenanthroline-catalyzed arylative cyclization of o-(1-alkynyl)thioanisoles: synthesis of 3-arylated benzo[b]thiophenes

- Arylative cyclization of o-(1-alkynyl)thioanisoles with aryl iodides is featured.
- [Pd(phen)2][PF6]2 works as a catalyst, and organosulfur-containing functional groups do not hamper the catalytic reactions.
- A range of 3-arylated benzo[b]thiophenes are provided.
- The reaction involves the cleavage of the carbon-sulfur bond.

The arylative cyclization of o-(1-alkynyl)thioanisoles with aryl iodides in the presence of catalytic amounts of [Pd(phen)2][PF6]2 resulted in the efficient formation of 3-arylated benzo[b]thiophenes, and a range of aryl iodides with electron-donating or -withdrawing groups could be used. While this reaction proceeded in the presence of aromatic and aliphatic groups on the terminal alkynyl carbon atom, silyl and alkoxycarbonyl groups hampered the reaction. Furthermore, this method could be extended to the synthesis of 3-arylated indoles from N,N-dimethyl-o-(1-alkynyl)aniline. All these reactions proceeded smoothly via cleavage of the carbon-heteroatom bond. In addition to the desired cyclization products, the use of a o-(hydroxypropyl)phenylmethyl substituent on the sulfur atom afforded isochroman, which should be formed by the intramolecular attack of a hydroxy group onto the benzylic carbon atom.

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