R1aLarabinofuranosyl

tube at 190 to 220°C, giving rise to a mixture of 50 (31%), 51 (11%), and illicinol (33) (13%), one of the chemical constituents of the leaves of I. arborescens. Compounds 50 and 51 were regarded as the products formed by the Claisen rearrangement of 33 derived from 37b, because 37b was again heated at the same temperature to yield 50 and 51 in 50 and 12% yields, respectively. Illicinol (33) was considered to be formed from 37 irreversibly, but a detailed mechanism was not proposed. In contrast, irradiation of 37b in ether at 20 to 30°C with a 400-W high-pressure mercury lamp afforded a mixture of novel tricyclic and tetracyclic products 52 (24%), 53 (11%), and 50 (15%). In addition, illicinol (33) was irradiated under the same conditions for 30 minutes to give illicinone A (37) (19%), 52 (28%), 53 (11%) as racemates, and 50 (16%). Irradiation of 33 for 10 minutes yielded 37 in 44% yield, but after 1 hour, 37 was not detected in the products. Thus, transformation from illicinol (33) to illicinone A (37) was photochemically correlated, whereas the reverse transformation occurred thermally. These chemical results are most likely to throw light on the biogenesis of nonaromatic prenylated C6-C3 compounds from illicinol A.

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