Backbone rearrangements of methyl (-)-kaur-9(11)-en-19-oate and its epoxide: structures of two diterpenes of a new skeletal type

1H and13C NMR signal assignments of a novel Baeyer-Villiger originated diterpene lactone

“…Besides, the signals corresponding to the ketone, the acid and the endocyclic double bond of the starting material were not present in the NMR spectra of the product. An analysis of the 13 13 , a kaurane diterpene bearing a  9 -11 double bond could produce zoapatline-type diterpene lactones, such as tetrachyrin (6), 3 in the course of a rearrangement under acid catalysis. In such rearrangement, a methyl group migration occurs from C-10 to C-9 and the carboxyl group at C-19 generates a C-4/C-10 -lactone.…”

“…In such rearrangement, a methyl group migration occurs from C-10 to C-9 and the carboxyl group at C-19 generates a C-4/C-10 -lactone. Thus, the skeleton structure elucidation started from the comparison of the 13 C NMR literature data of 6 14 with those of 5, beside careful analysis of data of 5, obtained from heteronuclear 1 H, 13 C-HMBC spectra. The signal at υ C 178.9 ppm was assigned to C-19 and the C-18 methyl group was assigned to signals at υ H 1.05 and υ C 15.7 ppm.…”

“…NMR spectra were recorded on a Bruker DRX 400-AVANCE spectrometer operating at 400 MHz for 1 H NMR and at 100 MHz for 13 C NMR in CDCl 3 at room temperature; ca 20 mg of compounds were dissolved in 0.5 ml of the solvent and transferred into a 5-mm NMR tube. TMS was used as internal reference.…”

“…Norketone 4 was obtained from grandiflorenic acid (3) by oxidation with NaIO 4 and catalytic amount of OsO 4 . 4 For the 13 C NMR data (100 MHz, CDCl 3 ), see Table 1. (5): the norketone 4 (200 mg, 0.66 mmol) in anhydrous dichloromethane (10 ml) was added at 0°C to a solution of trifluoroperacetic acid (CF 3 CO 3 H) in dichloromethane prepared in situ by adding anhydrous trifluoroacetic anhydride (14 ml) to 30% aqueous hydrogen peroxide (2.5 ml) in anhydrous dichloromethane (15 ml) at 0°C.…”

“…The organic layers were dried over anhydrous sodium sulfate and concentrated under reduced pressure. The recovered residue was subjected to column 13 C NMR data (100 MHz, CDCl 3 ), see Table 1.…”