Cascade transformation of 2-(diazoacetyl)-2 H -azirines to 2-aroyl-3-hydroxy-1 H -pyrroles via condensation with aromatic aldehydes

The Cs 2 CO 3 -induced condensation of 2-(diazoacetyl)-2 H -azirines with aromatic aldehydes does not result in the formation of an azirinyl-substituted β-hydroxy-α-diazocarbonyl compound, but is accompanied by a tandem intramolecular cyclization involving the hydroxy group and the C=N bond of the azirine to form a bicyclic intermediate, a 4-diazo-2-oxa-7-azabicyclo[4.1.0]heptan-5-one derivative. The acid-catalyzed transformation of which leads to 2-aroyl-3-hydroxy-1 H -pyrroles.