Some of these chemical reactions were a part of my PhD project thirty-two years ago. It was one of the most creative periods of my life. I have done this page to prevent forgetting it. You can find more information in the original publications in Polish Journal of Chemistry.
Regioselectivity of furan oxidation induced by neighboring hydroxyl groups
W. M. Daniewski, W. Kroszczyński, J. Król, Polish J. Chem., 57, 483, (1983)
Abstract
Furandiol and lactarorufin A are known sesquiterpenes isolated from the fungus Lactarius necator and from other fungi of the Lactarius family:
Oxidation of the furane ring of furandiol showed a profound effect of neighboring hydroxyl groups on regioselectivity of this reaction.
The oxidizing agent was m-chloroperbenzoic acid, mCPBA.
Protection of the secondary hydroxyl group of furandiol by acetylation produced furandiol 8-acetate. Oxidation of this protected compound proceeded in a regioselective manner to yield only one isomer. Its reduction with sodium borhydride afforded lactarorufin A 8-acetate. The latter was the only product of the synthesis.
Acetyl-protected hydroxyl group of furandiol is here the regioselective control element. And the tertiary hydroxyl group is an activating group, the another regioselective control element. One more;
Protection of the secondary hydroxyl group of furandiol causes the m-chloroperbenzoic acid molecule to form a hydrogen bond with the tertiary hydroxyl group. This gives rise to oxidation at the position 5, "up".
But when the secondary hydroxyl group of furandiol is not protected, it becomes the regioselective control element itself. It becomes the activating group, because the hydrogen bond forms with the secondary hydroxyl group:
And therefore, the main final product is not lactarorufin A (on the right), but so called "reversed" lactarorufin A, with the lactonic carbonyl in C-13 position ("down", as on the left):
The possibility of directing the regioselectivity can be useful synthetically.
The conclusion of this work is that lactarorufin A can be formed from furandiol in the biogenesis.
