| Abstract
| - The goal of the total synthesis of guanacastepene A served as a focus to bring together severalchemical inquiries. One involved the synthesis of fused 5,7-hydrazulenones (see structure 20).Another issue had to do with the mechanistic intermediates in reductive cyclizations (see 17 to 18and 19). The total synthesis required a mastery of an intramolecular Knoevenagel condensation ofa β,γ-unsaturated ketone (see compound 41). Actually, cyclization was best accomplished whenthe terminal double bond of 41 was first converted to an epoxide. Further issues related to thestereochemistry at C5 and, rather surprisingly, the propensity for β-face acetoxylation at C13.Crystallographic verification of the assigned β-stereochemistry at C13 is provided. Finally, a routeto optically active material is provided (see compound 20). A key element in this construction wasan enantioselective addition of isopropenyl cuprate to 2-methylcyclopentenone (see compound 99).
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