Enantiodivergent Synthesis of Either Enantiomer of ABCDE-Ring Analogue of Antitumor Antibiotic Fredericamycin A via Intramolecular [4 + 2] Cycloaddition Approach

An intramolecular enantiodivergent synthesis of both enantiomers of the ABCDE-ring analogue 22 of fredericamycin A is reported. Key steps involve an intramolecular [4 + 2] cycloaddition of 17 and an aromatic Pummerer-type reaction of 19. A lipase-catalyzed enantioselective desymmetrization of prochiral diol 2 using 1-ethoxyvinyl 2-furoate 3 led to the pivotal intermediate (R)-4.