Domino Michael/Retro‐Michael/Mukaiyama‐Aldol Reactions of 1,3‐Bis‐Silyl Enol Ethers with 3‐Acyl‐ and 3‐Formylbenzopyrylium Triflates – Synthesis of Functionalised 2,4′‐Dihydroxybenzophenones
The reaction of 1,3-bis-silyl enol ethers with 3-acyl- and 3-formylbenzopyrylium triflates, which can be generated in situ from 3-acyl- and 3-formylchromones, affords a great variety of functionalised 2,4′-dihydroxybenzophenones and 4-(2-hydroxybenzoyl)salicylates. These products are formed by a domino Michael/retro-Michael/Mukaiyama-aldol reaction. This methodology is successfully applied to the synthesis of novel UV-A/B and UV-B filters. Three 4-(2-hydroxybenzoyl)salicylic acids show a good in vitro activity in a selectin bioassay. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)