Total Synthesis of Indolizidine Alkaloids via Nickel-Catalyzed (4 + 2) Cyclization

Improved Total Synthesis of Indolizidine and Quinolizidine Alkaloids via Nickel-Catalyzed (4 + 2) Cycloaddition

A Ni-catalyzed (4 + 2) cycloaddition of bicyclic 3-azetidinones and alkynes was developed to access indolizidine and quinolizidine alkaloids. A key element was the development of a diazomethylation procedure that allows the efficient synthesis of bicyclic azetidinones from pyroglutamic and 6-oxopiperidine-2-carboxylic acid. A ligand screening led to improved regioselectivity and enantiopurity during the Ni-catalyzed (4 + 2) cycloaddition. This straightforward methodology was leveraged to synthesize (+)-ipalbidine, (+)-septicine, (+)-seco-antofine, and (+)-7-methoxy-julandine.

Diastereoselective Synthesis of Tetrahydrofurano[2,3-g]indolizidine and 8-Aminoindolizidines from L-Asparagine

8-Aminoindolizidines were synthesized from L-asparagine as the chiral starting material. The key dibenzylamino succinimide intermediate was synthesized in two steps. Three homologs of chiral hydroxylactams tethered with hydroxyalkene were synthesized from the succinimide via a sequence involving N-alkylation, cross olefin metathesis and hydride reduction. The dibenzylamino group gave the stereocontrol of the key N-acyliminium ion cyclization of these hydroxylactams. 5-Substituted-aminoindolizidines were synthesized with high diastereoselectivity at C6. A tandem cyclization of N-(6-hydroxyhex-3-en-1-yl)-g-hydroxylactam resulted in formation of tetrahydrofurano[2,3-g]indolizidine system.

A Concise Total Synthesis of Dehydroantofine and Its Antimalarial Activity against Chloroquine-Resistant Plasmodium falciparum

The total synthesis of dehydroantofine was achieved by employing a novel, regioselective, azahetero Diels-Alder reaction of easily accessible 3,5-dichloro-2H-1,4-oxazin-2-one with 14 a as a key step. Furthermore, it is demonstrated that dehydroantofine is a promising candidate as a new antimalarial agent in a biological assay with chloroquine-resistant Plasmodium falciparum.

Biologically active indolizidine alkaloids

Indolizidine alkaloids are chemical constituents isolated from various marine and terrestrial plants and animals, including but not limited to trees, fungi, ants, and frogs, with a myriad of important biological activities. In this review, we discuss the biological activity and pharmacological effects of indolizidine alkaloids and offer new avenues toward the discovery of new and better drugs based on these naturally occurring compounds.

Sterically enriched bulky 1,3-bis(N,N′-aralkyl)benzimidazolium based Pd-PEPPSI complexes for Buchwald–Hartwig amination reactions

A simple and efficient synthesis of a series of unexisting Pd-PEPPSI complexes is summarized. These complexes are exploited for their high catalytic activity towards Buchwald–Hartwig amination.