213
O
O
O
O
O
O
O
AcO
AcO
HO
O
50 (isopetasol)
O
O
O
OTs
1079
1080
1081
1082
1083
Scheme 6 Synthesis scheme for isopetasol (50) by Torii’s group
O
O
OH
O
5 (dehydrofukinone)
2
O
O
O
O
270 (furanoeremophil-9-ene)
1086 (furanoeremophilone)
7
1084
1085
Scheme 7 Synthesis scheme for eremophila-9,11-dien-8-one (2), dehydrofukinone (5),
furanoeremophil- 9-ene (270), and furanoeremophilone (1086) by Hagiwara et al.
5.4 Synthesis of Isopetasol
Torii et  al. synthesized isopetasol (50) starting from a tricyclic lactone 1079 by
introduction of a cis-dimethyl group through cyclopropanation (1080 to 1081) and
methylation (Scheme 6) [318]. The intermediate ketone 1082 was converted to
isopetasol (50) in several steps via 1083.
5.5 Synthesis of Eremophila-9,11-dien-8-one,
Dehydrofukinone, and Furanoeremophilanes
Hagiwara et al. reported syntheses of eremophila-9,11-dien-8-one (2) and dehydrofukinone (5) starting from bicyclic enone 1084 via 1085 obtained by an aldol reaction. Furanoeremophil-9-ene (270) and furanoeremophilone (1086) were also
prepared from compound 1084 (Scheme 7) [319].
Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity…