Biomimetic synthesis of the tetracyclic core of berkelic acid.
Acid-catalyzed condensation of 2,6-dihydroxybenzoic acid 3 with ketal aldehyde 14 in methanol at 25 degrees C, followed by CH2N2 esterification, gave a 4:1:4:1 mixture of diastereomers 15b-18b in 60% yield. Equilibration of this mixture with TFA in CDCl3 provided tetracycle 15b (83% yield) with the complete skeleton of berkelic acid. A similar condensation at 0 degrees C afforded 15b-18b and a reduction product 19b, which was probably formed by a 1,5-hydride shift.
Zhou
Jingye
J
Department of Chemistry, MS 015, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
Snider
Barry B
BB
D006576:Heterocyclic Compounds, 4 or More Rings / Q000138:chemical synthesis*; D015394:Molecular Structure; D013141:Spiro Compounds / Q000138:chemical synthesis*
D006576:Heterocyclic Compounds, 4 or More Rings; D013141:Spiro Compounds; C520589:berkelic acid