A simple synthesis of (+)- and (−)-alkaloid 241D and C-4 epimers

A Simple Stereoselective Route to α‐Trifluoromethyl Analogues of Piperidine Alkaloids

“…If deprotection were to occur first, the diequatorial conformer 38 , liberated from A(1,3) strain, would be expected as the stable intermediate. In this case, and as already observed with similar nonfluorinated systems,12b,22 an axial hydride attack should predominate, mostly giving the cis , cis ‐piperidinol 37 . The inversion of the sequence should entail an equatorial hydride attack on ketone 36 , due to significant steric hindrance, but still leading after deprotection of the intermediate 39 to the same all ‐ cis reaction product 37 .…”

Direct Asymmetric Synthesis of β-Amino Ketones from Sulfinimines (N-Sulfinylimines). Synthesis of (−)-Indolizidine 209B

“…The availability of small, easily manipulated chiral building blocks and templates has had a significant impact on the asymmetric syntheses of biologically and pharmaceutically valuable molecules. , Toward this objective, Troin and co-workers introduced the ketal of ( S )-(+)-4-amino-2-pentanone 5 and its enantiomer for the asymmetric synthesis of cis -2,6-disubstituted protected 4-oxo piperidines 6 . On treatment with various aldehydes, followed by acid, 5 undergoes a facile intramolecular Mannich reaction to afford 6 in good yield and high diastereoselectivity (Scheme 3).…”

Enantiodivergent Approach to the Synthesis of Cis-2,6-Disubstituted Piperidin-4-ones

“…Thus, alkaloid (+)-241D ( 11 ), isolated from the methanolic skin extracts of the Panamanian poison frog Dendrobates speciosus , was synthesized by reduction of 7f with lithium borohydride in MeOH at 0 °C, in 69% yield after column chromatography purification, as a single stereoisomer (Scheme ). Opposite relative facial selectivity was observed in the reduction of compound ent - 7j with L-Selectride at low temperature, leading in this case to (−)-lasubine II ( 12 ) in 70% yield, a natural product isolated from plants of the Lythraceae family (Scheme ).…”