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The versatility of the natural products (2S,3S)- and (2S,3R)-3-hydroxy-5-oxotetrahydrofuran-2,3-dicarboxylic acids (1 and 2), isolated in large amounts from tropical plant sources, has been demonstrated by the construction of 3-substituted and 3,4-disubstituted chiral pyrrolidine-2,5-diones. The absolute configurations of chiral pyrrolidine-2,5-diones have been ascertained using chiroptical spectroscopic methods and/or single-crystal XRD data. A combination of different reaction strategies delivering a diverse matrix of fused heterocyclic ring systems is presented. The pyrrolo­[2,1-a]­isoquinoline alkaloid (+)-crispine A possesses a wide range of pharmacological activities including antidepressant, antiplatelet, antileukemic, and anticancer activities. The analogues of indolizino­[8,7-b]­indole alkaloids (+)- and (−)-harmicine show strong antileishmanial, antinociceptive, PDE5-inhibitory, antimalarial, and antiviral activities. The bicyclic furo­[2,3-b]­pyrrolo skeleton is present in many natural products. Thus, the uniqueness of relatively cheap, naturally occurring chiral 2-hydroxycitric acid lactones as chirons has been demonstrated by the construction of some important molecular skeletons that are otherwise difficult to synthesize.

Dedicated to Professor Ibrahim Ibnusaud for his outstanding contributions in the field of organic synthesisDue to the high reactivity of cyclopropanes, different methods have been developed for their stereo-and regio-controlled ring-opening reactions to achieve a variety of synthetically useful targets. The traditional methods for the ring-opening include thermolysis, use of oxidants, transition metals or radical precursors in which many of them encounter various difficulties. In the past several years, visible-light-mediated photoredox reactions received considerable attention for various organic transformations. Several methodologies have been developed in recent times for the visible-light-mediated ring-opening reactions of cyclopropanes. Considering the synthetic potential of this class of reactions, we provide a summary of various methodologies developed for the cyclopropane ring-opening reactions under visible-light photoredox catalysis.

As a naturally occurring small-molecule, various optical isomers of chiral pyrrolo[2,1-a]isoquinoline alkaloid crispine A represent a potential class of chiral molecules in contemporary organic chemistry, and possess diverse biological activities. The range of pharmacological activities include antidepressant, antiplatelet, antileukemic, and anticancer activities. This review provides an overview of the literature on the strategies, employed in the synthesis of crispine A in their racemic and enantiopure forms via Bischler-Napieralski cyclization, Pictet-Spengler cyclization, N-Alkylation/Acylation-cyclization, Oxidative cyclization, and Asymmetric hydrogenation in the period of 1931-2021. This study accentuates the need for the developing more effective synthesis, and search for involved biological applications for the pyrroloisoquinoline class of natural product. Attention has been drawn towards the use of relatively less documented but easily accessible naturally occurring diastereomeric scaffolds namely, garcinia and hibiscus acids. These lactones obtained from (+)and (À )-2-hydroxycitric acids bearing chemically amenable functional groups are investigated as an ideal choice for the enantiopure synthesis of the (À )-(R)-and (+)-(S)-Crispine A structural frame work.

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