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Divergent Synthesis of Amino‐Substituted Indolizidine Alkaloids, Decahydropyrazino[2,1,6‐ cd ]pyrrolizine Triols, and (–)‐Pochonicine Stereoisomers
Author(s) -
Salunke Rahul Vilas,
Ramesh Namakkal G.
Publication year - 2020
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.202000194
Subject(s) - indolizidine , chemistry , intramolecular force , pyrrolizidine , diastereomer , stereochemistry , ring (chemistry) , intramolecular reaction , amination , reagent , organic chemistry , alkaloid , catalysis
A reagent‐directed divergent synthesis of three skeletally distinct compounds, namely, amino‐substituted indolizidine alkaloids, decahydropyrazino[2,1,6‐ cd ]‐pyrrolizine triols and (–)‐pochonicine stereoisomers have been accomplished from a single precursor. Tri‐ O ‐benzyl‐ d ‐glucal was converted into a diastereomeric mixture of homoallylic alcohols through a seven‐step sequence developed earlier in our lab. Intramolecular iodo‐amination of the homoallylic alcohols proceeded through a 5‐ exo‐tet ring opening of initially formed iodonium ion to give the iodo‐substituted pyrrolizidine {[5,5‐]‐fused} derivatives. Upon exposure to AgOAc, these iodo‐pyrrolizidines underwent a ring enlargement under the reaction condition and delivered polyhydroxylated indolizidine {[5,6]‐fused} derivatives as the main products. On the other hand, when the iodo‐pyrrolizidines were treated with NaH, a smooth intramolecular substitution reaction took place resulting in the formation of novel decahydropyrazino[2,1,6‐ cd ]pyrrolizine triols in good yields. Diversely, epoxidation of the homoallyic alcohols followed by intramolecular ring opening and subsequent synthetic transformations delivered stereoisomers of (–)‐pochonicine. The structure and stereochemistry of the final compounds were established through detailed 2D‐NMR analysis.