Total synthesis of (-)-kainic acid and (+)-allo-kainic acid through SmI2-mediated intramolecular coupling between allyl chloride and an α,β-unsaturated ester

Samarium(ii) iodide-mediated reactions applied to natural product total synthesis

Natural product synthesis remains a field in which new synthetic methods and reagents are continually being evaluated. Due to the demanding structures and complex functionality of many natural products, only powerful and selective methods and reagents will be highlighted in this proceeding. Since its introduction by Henri Kagan, samarium(ii) iodide (SmI₂, Kagan's reagent) has found increasing use in chemical synthesis. Over the years, many reviews have been published on the application of SmI₂ in numerous reductive coupling procedures as well as in natural product total synthesis. This review highlights recent advances in SmI₂-mediated synthetic strategies, as applied in the total synthesis of natural products since 2004.

Natural product synthesis remains a field in which new synthetic methods and reagents are continually being evaluated.

Marine Excitatory Amino Acids: Structure, Properties, Biosynthesis and Recent Approaches to Their Syntheses

This review considers the results of recent studies on marine excitatory amino acids, including kainic acid, domoic acid, dysiherbaine, and neodysiherbaine A, known as potent agonists of one of subtypes of glutamate receptors, the so-called kainate receptors. Novel information, particularly concerning biosynthesis, environmental roles, biological action, and syntheses of these marine metabolites, obtained mainly in last 10–15 years, is summarized. The goal of the review was not only to discuss recently obtained data, but also to provide a brief introduction to the field of marine excitatory amino acid research.

Total Syntheses of (+)-α-Allokainic Acid and (-)-2- epi-α-Allokainic Acid Employing Ketopinic Amide as a Chiral Auxiliary

Asymmetric Michael reaction of iminoglycinate 4 to α,β-unsaturated esters had been developed with >98:<2 diastereoselectivity. A reverse of diastereoselectivity for Michael reaction could be achieved by the replacement of lithium enolate with magnesium enolate. This methodology was applied to the total syntheses of (+)-α-allokainic acid 1 and (-)-2- epi-α-allokainic acid 6 each in 11 synthetic steps starting from 4 in 17.8 and 18.0% yields, respectively.

Synthesis of Kainoids and C4 Derivatives

A unified stereoselective synthesis of 4-substituted kainoids is reported. Four kainic acid analogues were obtained in 8-11 steps with up to 54% overall yields. Starting from trans-4-hydroxy-l-proline, the sequence enables a late-stage modification of C4 substituents with sp² nucleophiles. Stereoselective steps include a cerium-promoted nucleophilic addition and a palladium-catalyzed reduction. A 10-step route to acid 21a was also established to enable ready functionalization of the C4 position.

Enantioselective total synthesis of (-)-kainic acid and (+)-acromelic acid C via Rh(i)-catalyzed asymmetric enyne cycloisomerization

A diversity-oriented synthetic strategy was developed for the total synthesis of kainoid amino acids, which led to the enantioselective synthesis of (-)-kainic acid and the first total synthesis of (+)-acromelic acid C. Rh(i)-catalyzed asymmetric enyne cycloisomerization served as the key reaction in this strategy for the rapid construction of highly functionalized lactam, and the resulting vinyl acetate moiety was further utilized as a versatile building block for the installation of both isopropylidene and 2-pyridone units existing in natural kainoids.