Iron-catalyzed cascade one-pot reaction between azlactones and O-acetyl oximes to afford 6H-pyrrolo[3,2-d]oxazole and pyrrol-2-one nucleus

Abstract

A unified and controlled cyclization reaction between azlactone and O-acetyl oxime is accomplished. Azlactone, with numerous reactive sites, reacts with the radically activated O-acetyl oxime. The reaction displays the remarkable selectivity of azlactone at the C-4 site rather than at the other reported active sites (C-2 and C-5). The substitution pattern at the C-4 position of the azlactone played a decisive role in determining the reaction pathway. Azlactones bearing a substituent at the C-4 position preferentially underwent cyclization to afford the product 6H-pyrrolo[3,2-d]oxazole nucleus, while azlactones without substitution at this position predominantly afforded the product pyrrol-2-one nucleus. A substantial increase in the product yield is observed upon the addition of DTBP.