Regioselective Synthesis of Pyrone-Annulated Sulfur Heterocycles by Aryl Radical Cyclization

Abstract

The tri-n-butyltin hydride mediated cyclization of a number of 4-(2′-bromophenoxymethyl)-7-methylthiopyrano[3,2-c]pyran-5-ones have been carried out to afford tetracyclic [6,6]pyranothiopyrans in 70-80% yield and good to excellent diastereoselectivity. The substrate ethers were obtained by a thio-Claisen rearrangement of the corresponding 4-(4′-aryloxybut-2′-ynyl)-6-methyl pyran-2-ones. The cis stereochemistry of the predominant diastereomer has been corroborated by single crystal X-ray analysis.

Keywords

4-mercapto-6-methyl pyran-2-one - tri-n-butyltin hydride - 6-endo cyclization - azobisisobutyronitrile - thio-Claisen rearrangement

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