First enantiospecific Baker–Venkataraman-rearrangements aiming at the total synthesis of chiral anthrapyran antibiotics

The base-catalyzed acyl transfer (Baker–Venkataraman reaction) of chiral 2-acetyl-1-hydroxyanthraquionone esters 6 of 2-methylbutanoic acid or 11 of O-allyl lactic acid proceeds with virtually no racemization to ketides 7 and 12. The subsequent acid-catalyzed cyclization to the chiral anthra[1,2-b]pyran antibiotics such as (S)-1″-11-dideoxyespicufolin 8 or 13 also occurs with a very low racemization.

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(S)-2-Acetyl-9,10-dihydro-9,10-dioxoanthracen-1-yl 2-(allyloxy)propanoateC22H18O6[α]D20=-16 (c 1.03, CHCl3)

2-(4-Allyloxy-3-oxo-pentanoyl)-1-hydroxy-anthraquinoneC22H18O6[α]D20=-88 (c 0.52, CHCl3)

2-(1-(Allyloxy)ethyl)-4H-naphtho[2,3-h]chromene-4,7,12-trioneC22H18O6[α]D20=-87 (c 0.52, CHCl3)