Lewis-acid promoted rearrangement of σ-homo-o-benzoquinones to α-tropolone derivatives: application to regiocontrolled syntheses of MY3-469 and isopygmaein

Reaction of various σ-homo-o-benzoquinones, e. g.42, with BF3·Et2O results in the formation of the tropolonoboron difluoride derivatives, e. g.43, of the isomeric α-tropolones, e.g. isopygmaein 33.