After a series of optimization for the reaction conditions (reagents, reaction temperature, etc.), treatment of the sulfonates 4, 8, 13 and 15 with 8% NaOH (room temperature, 24h) via a semipinacol rearrangement afforded the corresponding C-nor compounds 5, 9, 12 and 16, as the major of a pair of epimer at C-16, to an excellent extent, in 95%, 92%, 100% and 90% yield, respectively. The 12,13-seco compounds 21 and 22 (23) were obtained in 20% and 60% yield, respectively, by treating 5 with Br2–glacial HOAc (room temperature, 24 h). Treatment of the C-nor compounds 5 or 6, 16 or 17, and 28 from 10 with SOCl2-anhydrous benzene (room temperature, overnight) afforded the 12,13-seco compounds 24, 26 and 30 in 70% or 100%, 40% and 66% yield, respectively. When treatment of the C-nor compound 29 from 9 under same conditions gave the 12,13-seco products 30, 31 and 32 in 33%, 26% and 20% yield. When treating 21 or 24, and 26 with 5% KOH in EtOH afforded the 12,13-seco compounds 25 and 27 quantitatively, respectively. The compound 31 converted to 30 quantitatively by treatment with Na2CO3 in MeOH. All of the new compounds were isolated and fully characterized.

Treatment of 3-acetylyunaconitine 2 from yunaconitine 1 with NBS at 40C for 12h afforded the 3-acetylyunaconitine azomethine 3 (48%). Reaction of 3 with CHsI in MeOH at room temperature overnight gave the iminium salt 4 (100%). Unexpectedly, treatment of 4 with 5% NaOH in methanol at room temperature for 20min produced the rearrangement alkaloid 5 (38%) besides other unidentified compounds. Acetylation of 5 with AczO/pyridine containing a small amount of TsOH gave its two derivatives 6 (28%) and 7 (56%). The structure of 5 was confirmed using 2D NMR spectra and single crystal X-ray analysis of its acetyl derivative 7. 2002 Elsevier Science Ltd. All rights reserved.

Treatment of 14-methylsulfonyl pseudaconine 3 with DMF-NaOH at 1508C for 10 h afforded the desired C-nor and 12,13-seco norditerpenoid alkaloids 16a-methoxyl ketone 7 (70%) and 16b-methoxyl ketone 8 (15%) as a pair of epimers. Reaction of 7 with Br2-HOAc at room temperature for 1.5-2 h produced the phenols 9 (40%), 10 (10%) and 13 (29%). Whereas, treatment of 8 with Br2-HOAc under same conditions as the case for 7 gave phenolic compound 9 (38%) besides the by-product a-bromoketone 14 (25%).

Oxidation of pseudaconine 8, a norditerpenoid alkaloid, with HIO4 led to a series of novel interesting products, depending greatly on reaction medium and work-up conditions. Treatment of 8 in MeOH-H2O (1:1) with NaIO4 gave compounds 10 and 11, but compound 12 was obtained quantitatively when the final reaction solution was alkalized with conc. NH4OH. The imine 12 was also obtained in 100% yield by treating 8 in 5% HCl solution with NaIO4 followed by alkalizing the reaction products to pH.9 with conc. NH4OH. When the work up pH was 7-8, only N,O-mixed acetal-ketal 13 was formed in 96% yield, which was converted quantitatively to 12 by further alkalizing. When the reaction mixture was alkalized to pH 7-8 with Na2CO3, a hemiacetalketal 14 was afforded quantitatively, which was converted to 15 in 87% yield by further treatment with Na2CO3 or 5% NaOH methanol. Compound 15 could be converted back to 14 by treatment with 10% HCl solution. Acetylation of the imine 12 gave the compounds 16 and 17 in 15% and 19% yields, respectively. All of the new compounds were isolated and fully characterized.

New access to the 7, 17-seco norditerpenoid alkaloids 9 (60%) from yunnaconitine (5), as well as 14 (46%) and 15 (22%) from isotalatizidine (10), via selective hydrolysis, chlorination and reduction with NaBH4 is described.