Total synthesis of indole and dihydroindole alkaloids. III. Transannular cyclization of carbomethoxydihydrocleavamine and carbomethoxycleavamine derivatives. Approach to vinca and iboga alkaloids

Dihydropyridines in synthesis and biosynthesis. IV. Dehydrosecodine, in vitro precursor of indole alkaloids

“…Chromatography on silica gel afforded 18 (41 mg, 20% yield). The physical data were identical with those of the compound prepared from N-methyl-3-ethyl-l,2-dihydropyridinetricarbonylchromium(0) (7).…”

“…For the 1 ,2-dihydropyridine isomer, 9, enamine behaviour, via P-alkylation, should lead to the N-benzylcleavamine derivative 11 or by transannular cyclization to the pseudo-vincadifformine 12 (7,8). Alternatively, the dehydrovincadine 13 would arise via 8-alkylation (Scheme 3).…”

Synthesis of (−)-Pseudotabersonine, (−)-Pseudovincadifformine, and (+)-Coronaridine Enabled by Photoredox Catalysis in Flow

“…Chief among our interests was the alkaloid (−)-pseudotabersonine 2 (Scheme 1 ), which was first generated from catharanthine by Gorman et al by refluxing catharanthine in glacial acetic acid for 16 h. 13 Unfortunately, catharanthine’s potential as a chiral pool material in such investigations was hampered by an estimated 90% racemization of the starting material and only 20% yield. 14 Kutney et al also reported formation of pseudotabersonine from catharanthine through a two-step reduction 10 -oxidation 15 procedure, affording 2 in 18% overall yield, also with low enantiopurity. 14 Alternative examples of pseudotabersonine total syntheses are exclusively racemic.…”

Alcaloïdes bis‐indoliques de Catharanthus ovalis

“…En effet, une cyclisation C(7)-+C(3) s'observe couramment lors de l'oxydation en position 3 de composes monoindoliques du type ibogane tktracyclique [30]; la formation de quantite non negligeable de La structure 24 pourrait ainsi deriver, par oxydation du group H,C-N, et de la position 3', de la leurosidine (31)5) dont le groupe hydroxyle tertiaire en C(20')…”