New classes of amidine, indolizidine and quinolizidine alkaloids from a poison-frog, (dendrobatidae)

Synthesis of Chiral Aza‐[n.2.1] Skeletons by Separable Epimers of Intramolecular [3+2] Cross Cycloaddition of Cyclopropane 1,1‐Diesters with Chiral Sulfinylimines

“…[9] In this paper, it was used in Lewis acid catalyzed intramolecular [3 + 2] cross The epimers (1 a/1 a') were synthesized from (R)-2methyl-2-propanesulfinamide and its corresponding aldehyde, which could not be separated by silica gel column chromatography. When 1 a/1 a' was treated with Sc(OTf) 3 in DCM at room temperature, the desired products 2 a and 2 a' were smoothly formed and they could be easily separated by the silica gel column chromatography [The retention factor value (R f ) of 2 a for thin layer chromatography inspection on silica gel plates was 0.40 and that of 2 a' was 0.51 in a solution of petroleum ether/ethyl acetate, 1:1.]. Thus, the chiral aza-[n.2.1] epimers could be obtained by using of (R)-2-methyl-2-propanesulfinamide via silica gel column chromatography.…”

A new approach to the 8b-azaacenaphthylene ring system

“…This [6.6.5]-tricyclic ring system was first found in crepidine (1, Fig. 2 Finally, in the 90s exochomine (3) 3 and the chilocorines A-C (e.g., 4), 4 dimeric ladybird alkaloids, were found to have the 8b-azaacenaphthylene ring system embedded in their structures. 1 Alkaloid (−)-205B (2), present in trace amounts in the skin of the neotropical frog Dendrobate pumilio, was isolated almost two decades later and shown to also have this ring skeleton.…”

Flexible synthetic routes to poison-frog alkaloids of the 5,8-disubstituted indolizidine-class I: synthesis of common lactam chiral building blocks and application to the synthesis of (-)-203A, (-)-205A, and (-)-219F

“…Hydrogenation of the double bond in 11 or 12 over 20% Pd(OH) 2 and then treatment of the resulting deblocked amino alcohols with trimethylaluminum under Weinreb's conditions [21] gave rise to the lactams 1 and 2 in 71% and 68% overall yields, respectively. To demonstrate the utility of the chiral lactam building blocks, we conducted the total synthesis of indolizidines (-)-203A [22] and (-)-205A [23] from 1, and (-)-219F [2] from 2, respectively (Scheme 3, Scheme 4). Removal of the silyl protecting group in 1 was performed by treatment with TBAF to afford the corresponding alcohol 13, which was converted to the homologated ester 14 via a two-step oxidation, followed by an Arndt-Eistert sequence of the resulting carboxylic acid.…”