Bismuth triflate-catalyzed Wagner-Meerwein rearrangement in terpenes. Application to the synthesis of the 18alpha-oleanane core and A-neo-18alpha-oleanene compounds from lupanes.
The use of bismuth(III) salts as catalysts for the Wagner-Meerwein rearrangement of lupane derivatives with expansion of ring E and formation of an additional O-containing ring is reported. This process has also been extended to other terpenes, such as the sesquiterpene (-)-caryophyllene oxide. When the reaction was performed with oleanonic acid, 28,13beta-lactonization occurred, without Wagner-Meerwein rearrangement. Under more vigorous reaction conditions, dehydration of the 3beta-hydroxyl group and subsequent additional Wagner-Meerwein rearrangement led to the selective synthesis of A-neo-18alpha-oleanene compounds, in very high yields.
Salvador
Jorge A R
JA
Laboratório de Química Farmacêutica, Faculdade de Farmácia, Universidade de Coimbra, 3000-295 Coimbra, Portugal. salvador@ci.uc.pt
Pinto
Rui M A
RM
Santos
Rita C
RC
Le Roux
Christophe
C
Beja
Ana Matos
AM
Paixão
José A
JA
D002384:Catalysis; D008698:Mesylates / Q000737:chemistry*; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013379:Substrate Specificity; D013729:Terpenes / Q000737:chemistry*; D014315:Triterpenes / Q000737:chemistry*; D053978:Pentacyclic Triterpenes
D008698:Mesylates; D009828:Oleanolic Acid; D012997:Solvents; D013729:Terpenes; D014315:Triterpenes; C413246:oleanane; C480546:lupane; D053978:Pentacyclic Triterpenes; C445789:Bi(OTf)3