219
OH
O
O
O
O
1131 (isoligularone)
+
1132
1102
1134
1133
O
Scheme 16 Synthesis scheme for isoligularone (1131) by Kraus et al.
5.13 Synthesis of (−)-(R)-Ligularenolide and (−)-(R)-PF1092C
The synthesis of eremophilan-12,8-olides was reported by Groot’s group (Scheme
17) [329]. Hence, (+)-(S)-carvone (1108) was subjected to conjugate addition and
annelation to afford enone 1135. Oxidative elimination sequences produced dienone 1136. The enolate of 1136 was condensed with ethyl pyruvate and cyclized to
give the desired (−)-(R)-ligularenolide (447). The intermediate 1135 was transformed to 1139 and (−)-(R)-PF1092C (1140) in several steps via 1137 and 1138.
Scheme 17 Synthesis scheme for (−)-(R)-ligularenolide (447) and (−)-(R)-PF1092C (1140) by
Groot’s group
Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity…
OH
O
O
O
O
1131 (isoligularone)
+
1132
1102
1134
1133
O
Scheme 16 Synthesis scheme for isoligularone (1131) by Kraus et al.
5.13 Synthesis of (−)-(R)-Ligularenolide and (−)-(R)-PF1092C
The synthesis of eremophilan-12,8-olides was reported by Groot’s group (Scheme
17) [329]. Hence, (+)-(S)-carvone (1108) was subjected to conjugate addition and
annelation to afford enone 1135. Oxidative elimination sequences produced dienone 1136. The enolate of 1136 was condensed with ethyl pyruvate and cyclized to
give the desired (−)-(R)-ligularenolide (447). The intermediate 1135 was transformed to 1139 and (−)-(R)-PF1092C (1140) in several steps via 1137 and 1138.
Scheme 17 Synthesis scheme for (−)-(R)-ligularenolide (447) and (−)-(R)-PF1092C (1140) by
Groot’s group
Chemical Constituents of Ligularia Species (Asteraceae) and Their Diversity…