It is well known that the cyclic diterpenoids in the acid medium lead to the formation of
compounds with rearranged carbon framework.
Taking into consideration the above mentioned statement, we report in the present
communication results on the acid induced rearrangements of methyl 12α,13α-epoxy-entisocopal-
l5β-oate dependent upon the reaction conditions. The interaction of ent-isocopalic
epoxide (1) with p-toluenesulfonic acid in chloroform on refluxing provided a mixture of two
diterpenic compounds (2) and (3). The unpolar compound (2) was identified as the rearranged
ent-isocopalate diene with an ent-verrucosin A carbon skeleton [2]. According to the NMR
spectrum, the polar product was the well known diterpene γ-lactone (3) [3].

Scheme 1
Reagents and conditions: (a) p-TsOH, CHCl3, reflux 4 h; (b) FSO3H, i-PrNO2, -78oC,
30 min, then MeOH.
Trasformation of the methyl ether (1) under super acide conditions (FSO3H, i-PrNO2, -
78oC, 30 min) gave the another mixture of two rearranged diterpenoids. The major compound
was identified as an aldehyde (4) (~70%) by comparison of its spectroscopic data (IR, 1H- and
13C-NMR) with those given in the literature [4]. The structure and stereochemistry of the
synthesized compound (2) were established on the basis of the spectral data.
References:
Coates, R. M. Prog. Chem. Org. Nat. Prod., 1976, 33, 73-230.
(a) Cimino, G.; Gavagnin, M.; Sodano, G.; Puliti, R.; Mattia, C. A.; Mazzarella, L. Tetrahedron, 1988, 44
(8), 2301-2310. (b) Zubia, E.; Gavagnin, M.; Crispino, A.; Martinez, E.; Ortea, J.; Cimino, G.
Experientia, 1993, 49 (3), 268-271.
Imamura, P. M.; Sierra, M, G.; Ruveda, E. A. J. Chem. Soc., Chem. Comm., 1981, 734-735.
(a) Basabe, P.; Diego, A.; Diez, D.; Marcos, I. S.; Urones, J. G. Synlett, 2000, 1807–1809. (b) Basabe, P.;
Diego, A.; Diez, D.; Marcos, I. S.; Mollinedo, F.; Urones, J. G. Synthesis, 2002, 1523–1529.