Eosin, blue LEDs and DIPEA are employed in a simple synthesis of (poly)cyclic O , O - and N , O -acetals.

A simple procedure for the synthesis of (poly)cyclic O , O - and N , O -acetals from various enol ethers, N -acyl enamines or Boc-protected enamines has been developed. The key step is a photocatalytic Stork-Ueno-type cylization using the very simple metal-free conditions of catalytic eosin, diisopropylamine in the green solvent ethanol with blue LED irradition.