Synthesis of (±)-aklavinone and (±)-auramycinone via electron-deficient o-quinonoid pyrones

Abstract

Dehydration of the formyl acid 3(R = H) with acetic anhydride in benzene at 80 °C generates the quinonoid pyrone 4 which can be trapped with norbornadiene, N-phenylmaleimide and enol silyl ethers; the adduct 6(R = Me, P = TES) and its 9-epimer 10 from 2-(triethylsilyloxy)propene are readily transformed into (±)-auramycinone 2(R = Me) whilst those [6(R = vinyl, P = TES) and its 9-epimer] from 2-(triethylsilyloxy)buta-1,3-diene are readily converted into the methyl ethers 24, 25, 33 and 34 of which 24, 33 and 34 are known to be readily converted into (±)-aklavinone 2(R = Et).