Reaction of 4,5,6,7-tetrahydrobenzofuran derivatives, model compounds of furanoeremophilanes, with p-dimethylamino-benzaldehyde (Ehrlich's reagent) under acidic conditions was studied both on TLC and in a flask. 4-Hydroxy, 4-methoxy, and 4-acetoxy derivatives showed a pink/purple color, while 7-hydroxy, 7-methoxy, and 7-acetoxy derivatives showed a dark green color. The reaction of a 4-oxo derivative was slow showing an orange color on TLC. 7-Oxo derivatives and benzofuran were negative to Ehrlich's test. It was shown that an intermediate cation corresponding to the pink color was generated from both 4- and 7-substituted derivatives except for the oxo-derivatives.
FieserLF, FieserM. (1967) Reagents for Organic Synthesis. Wiley, New York.
2.
For examples, (a) IshizakiY, TanahashiY, TakahashiT, ToriK. (1969) Furanoeremophilan-14β,6α-olide, a new furanosesquiterpene lactone from Ligularia Hodgsoni Hook, f. The structure and Nuclear Overhauser Effects. Journal of the Chemical Society, Chemical Communications, 551–552
3.
(b) TadaM, MoriyamaY, TanahashiY, TakahashiT. (1974) Furanoeremophilane-6β,10β-diol and its derivatives. New furanosesquiterpenes from Ligularia japonica Less. Bulletin of the Chemical Society of Japan, 47, 1999–2002
4.
(c) SatoT, MoriyamaY, NaganoH, TanahashiY, TakahashiT. (1975) New furanosesquiterpenes from Ligularia fischeri Turcz. 1β,10β-Epoxyfuranoeremophilan-6β-ol and its derivative. Bulletin of the Chemical Society of Japan, 48, 112–114
5.
(d) IshiiH, TozyoT, MinatoH. (1969) Studies on sesquiterpenoids-IX. Structure of ligularol and ligularone from Ligularia sibirica Cass. Tetrahedron, 21, 2605–2610.
6.
For examples, (a) NaganoH, TanahashiY, MoyiyamaY, TakahashiT. (1973) New furanoeremophilane derivatives from Farfugium japonicum Kitamura. Bulletin of the Chemical Society of Japan, 46, 2840–2845
7.
(b) KurodaC, MuraeT, TadaM, NaganoH, TsuyukiT, TakahashiT. (1982) 3β,6β-Bis(acyloxy)furanoeremophilan-14-als and -14-oic acids from Syneilesis palmata (Thunb.) Maxim. Bulletin of the Chemical Society of Japan, 55, 1228–1233
8.
(c) NayaK, NakagawaM, HayashiM, TsujiK, NaitoM. (1971) The constituents of Petasites japonicus Maxim. rhizomes. Tetrahedron Letters, 2961–2964.
9.
MartinA, LópezMD, EstebanMA, MeseguerJ, MuñozJ, FontanaA. (1998) Anatomical and ultrastructural studies of chemical defence in the sponge Dysidea fragilis.Marine Biology, 131, 639–645.
10.
(a) HanaiR, GongX, ToriM, KondoS, OtoseK, OkamotoY, NishihamaT, MurotaA, ShenY, WuS, KurodaC. (2005) Chemical and genetic study of Ligularia tongolensis, Ligularia cymbulifera, and Ligularia atroviolacea in the Hengduan Mountains of China. Bulletin of the Chemical Society of Japan, 78, 1302–1308
11.
(b) NaganoH, IwazakiY, GongX, ShenY, KurodaC, HanaiR. (2006) Chemical and genetic differentiation of Ligularia pleurocaulis in northwestern Yunnan and southwestern Sichuan Provinces of China. Bulletin of the Chemical Society of Japan, 79, 300–304
12.
(c) ToriM, HondaK, NakamizoH, OkamotoY, SakaokuM, TakaokaS, GongX, ShenY, KurodaC, HanaiR. (2006) Chemical constituents of Ligularia virgaurea and its diversity in southwestern Sichuan of China. Tetrahedron, 62, 4988–4995.
13.
LiuSW, DengDS, LiuJQ. (1994) Origin, evolution and distribution of Ligularia Cass. (Compositae). Acta Phytotaxonomica Sinica, 32, 514–524.
14.
KurodaC, UeshinoT, NaganoH. (2004) Ehrlich's reaction of furanoeremophilanes. Bulletin of the Chemical Society of Japan, 77, 1737–1740.
15.
Bisagnié, MarquetJ-P, BourzatJ-D, PepinJ-J, André-LouisfertJ. (1971) Furannes et pyrroles disubstitués en 2,3. XI. Réaction du chloracétaldéhyde sur les β-cétoesters: formation des furannes ou pyrroles attendus et de diacyl-1,4 cyclohexadiènes-1,4. Bulletin de la Société Chimique de France, 4041–4047.
16.
SekiM, SakamotoT, SuemuneH, KanematsuK. (1997) Total synthesis of (±)-furoscrobiculin B. Journal of the Chemical Society, Perkin Transactions1, 1707–1714.
17.
OhCH, ReddyVR, KimA, RhimCY. (2006) Nucleophile-assisted Pt-catalyzed cyclization of enynones: an acess to synthesis of highly substituted furans. Tetrahedron Letters, 47, 5307–5310.
18.
NovotnýL, KotvaK, TomanJ, HeroutV. (1972) Sesquiterpenes from Petasites.Phytochemistry, 11, 2795–2799.
19.
(a) TerabeM, TadaM, TakahashiT. (1978) Absolute stereochemistry of cacalol. Bulletin of the Chemical Society of Japan, 51, 661–662
20.
(b) ChenH-M, WangY-Y, MaoJ-M, CaiM-S, JiaZ-J. (1997) Syntheses and pharmacological activities of the derivatives of furanosesquiterpenes from Ligularia virgaurea.Planta Medica, 63, 299–302.
