Syntheses of Tetrahydrofurobenzofurans: A Synthesis of (+/-)-Aflatoxin B2

Article abstract of DOI:10.1021/jo00357a011

Aldehyde O-aryl oximes, on treatment with hydrogen chloride in tetrahydrofuran, are converted to 2-hydroxy-2,3-dihydrobenzofurans and their corresponding 4-chlorobutanol ketals.The major reaction pathway, a 3,4-oxaza Cope rearrangement, is accompanied by Beckmann fragmentation, the relative amount of which is sensitive to the stereochemistry of the oxime and the specific acid conditions.With appropriately substituted oximes, the 2,3,3a,8a-tetrahydrofuro<2,3-b>benzofuran ring system is efficiently prepared, as is demonstrated for the 4-hydroxy-6-methoxy derivative and its regioisomer.The former compound provides a total synthesis of alfatoxin B₂.