抄録
Dye-sensitized oxygenation of Nb-methoxycarbonyltryptamine(5) in methanol in the presence of rose bengal under ice-cooling(0-1°) gave 3a-hydroperoxypyrroloindole(6) in 40% yield. The hydroperoxide (6) was reduced with dimethylsulfide to the hydroxy derivative (7) and converted to ketoamide (8) and Nb-formylketoamine (9) along with 7 on treatment with silica gel. On the other hand, when 5 in thoroughly O_2-saturated formic acid was irradiated with a halogen lamp for 1 hr in the presence of proflavin hemisulfate, dimeric compounds (21 and 22) were obtained along with Na-formyl-3a-hydroxypyrroloindole (20) and oxidative 2,3-bond cleavage products such as 8 and 9 were not isolated. Pyrroloindole dimer(21) was obtained in 13-27% yield and can be separated into racemic and meso isomers: 21a, mp 255-256°; 21b, mp 282-284°. LiAlH_4 reduction of 21(a and b) in THF gave racemic folicanthine, mp 167.5-168.5°, in 29% yield. Reduction of 21b with LiAlH_4 in dioxane gave meso folicanthine in 60% yield. Hydrolysis of 21a by NaOH-MeOH gave deformyl derivative (23a) which was reduced with LiAlH_4 in THF to racemic chimonanthine in 29% yield from 21a. Similar treatment of 21b provided meso chimonathine. These results indicated that 21a was racemic form and 21b was meso form.
