210
Scheme 1 Synthesis scheme of ligularone (168) and other terpenoids by Yamakawa and Satoh
5.1 Synthesis of Ligularol (= Petasalbin), Ligularone,
and Related Compounds
There are several reports on the synthesis of ligularol (161) and its derivatives.
Among them the investigations by Yamakawa and Satoh, published in 1977–1981,
are introduced here [310–314].
The Diels-Alder reaction of 1049 with 1050 afforded 1051, which was converted
to 1052 and 1053 (Scheme 1). Dehydroxylation of 1053 gave both the cis and trans
diketones, 1054 and 1055, of which the latter was transformed further to
3β-hydroxyfuranoeremophilane (1056). Ligularone (168), 3β-furanoligularanol
(1057), and furanoeremophilane (160) were synthesized from 1052, 1054, and
1055, respectively [310, 311].
Another route to ligularone (168) and ligularol (161) was reported (Scheme 2)
[312]. The intermediate 1051 was converted to 1058, from which ligularone (168)
and ligularol (161) were synthesized. In addition, 1058 was converted to furanofukinol (1059) by stepwise reductions.
The furan derivative 1060, prepared by a similar method to that described above,
was used for the introduction of a double bond at C-1/C-10 (Scheme 3) [314]. Thus,
compound 1060 was converted to 1062 via 1061 in several steps. Decompostin
(278) and adenostylone (280) were synthesized from 1063.
M. Tori and C. Kuroda
Scheme 1 Synthesis scheme of ligularone (168) and other terpenoids by Yamakawa and Satoh
5.1 Synthesis of Ligularol (= Petasalbin), Ligularone,
and Related Compounds
There are several reports on the synthesis of ligularol (161) and its derivatives.
Among them the investigations by Yamakawa and Satoh, published in 1977–1981,
are introduced here [310–314].
The Diels-Alder reaction of 1049 with 1050 afforded 1051, which was converted
to 1052 and 1053 (Scheme 1). Dehydroxylation of 1053 gave both the cis and trans
diketones, 1054 and 1055, of which the latter was transformed further to
3β-hydroxyfuranoeremophilane (1056). Ligularone (168), 3β-furanoligularanol
(1057), and furanoeremophilane (160) were synthesized from 1052, 1054, and
1055, respectively [310, 311].
Another route to ligularone (168) and ligularol (161) was reported (Scheme 2)
[312]. The intermediate 1051 was converted to 1058, from which ligularone (168)
and ligularol (161) were synthesized. In addition, 1058 was converted to furanofukinol (1059) by stepwise reductions.
The furan derivative 1060, prepared by a similar method to that described above,
was used for the introduction of a double bond at C-1/C-10 (Scheme 3) [314]. Thus,
compound 1060 was converted to 1062 via 1061 in several steps. Decompostin
(278) and adenostylone (280) were synthesized from 1063.
M. Tori and C. Kuroda