Asymmetric syntheses of (8R,8aS)- and (8R,8aR)-8-hydroxy-5-indolizidinones:Two promising oxygenated indolizidine building blocks

Starting from the oxygenated piperidine building block 20,two synthetic approaches to new building blocks (8R,8aS)-and (8R,8aR)-8-hydroxy-5-indolizidinones 19a/19b and 15a/15b have been developed,respectively. The first one is based on the trans-diastereoselective reductive alkylation (dr = 93:7),followed by a four-step procedure; and the second one called for the RCM reaction on the N,O-acetal derived from a vinylation,which was followed by a pyrrole formation,and a stereocontrolled cis-selective (dr = 91:9) catalytic hydrogenation. Reduction of the diastereomer 15a produced (8R,8aR)-8-indolizidinol (18).

Visible-Light-Mediated Synthesis of Cyclobutene-Fused Indolizidines and Related Structural Analogs

Expedient assembly of unprecedented molecular scaffolds from readily accessible starting materials in a sustainable fashion is highly pursued in modern organic chemistry.Herein,the first catalytic intramolecular dearomative[2+2]cycloaddition of indoles or pyrroles with alkynes is achieved via visible-lightmediated energy-transfer catalysis.This method enables the synthesis of cyclobutene-fused indolizidines,which are otherwise challenging to access,in high yields with exclusive selectivity.The reaction profiles are well documented by density functional theory(DFT)calculations.In addition,this protocol can be extended to the synthesis of cyclobutane-fused indolizidines and related structural analogs.Diverse elaborations of the products are achieved.

One-pot tandem route to fused indolizidines and quinolizidines:Application in the synthesis of alkaloids and bioactive compounds

Fused indolizidines and quinolizidines are important skeletons in a variety of natural products and pharmacologically important compounds.A one-pot tan dem route from amide to fused indolizidines and quinolizidines is disclosed.This method is con ducted in mild conditions and shows well tolerance of functional groups.It is also easy to be scaled up to gram scale and can be applied smoothly to the total synthesis of alkaloids such as(±)-crispine A,(±)-xylopinine,(±)-desbromoarborescidine A,(±)-harmicine and other bioactive substances.

Concise synthesis of 1-epi-castanospermine

1-epi-Castanospermine（5） was synthesized from readily available 2,3,4,6-tetra-O-benzyl-1-deoxynojirimycin（11） in 9 steps and 21% overall yield, with selective debenzylation, Barbier reaction and reductive amination as the main reaction steps.