Assembly of multicyclic isoquinoline scaffolds from pyridines: formal total synthesis of fredericamycin A

Carbene-catalyzed enantioselective construction of a quasi-symmetrical spirocyclic hydroquinone with a minor chiral distinction

Constructing a nearly symmetrical chiral center with tiny chiral differences is a challenging task in asymmetric synthesis. The natural antibiotic fredericamycin A (FDM-A), a representative example, has a unique structure with a quasi-symmetrical spirocyclic hydroquinone and remains difficult to chemically synthesize. Herein we developed an N-heterocyclic carbene-catalyzed enantioselective hydroquinone formation reaction with desymmetrization of spirocyclic cyclopentene-1,3-diones to construct these challenging structures. Using our method, the asymmetric synthesis of FDM-A (previously requiring a 26-step or 32-step synthesis) was shortened to 11 steps. Several analogs of FDM-A were also readily made. Moreover, a more challenging all-carbon quaternary chiral center with minimal differences (H vs. D) in a remote position (6 atoms away from the chiral center) was also constructed to investigate the performance of the extremely weakly chiral small molecule.

Synthesis of a novel nanomagnetic N4 bis schiff base complex of copper(ii) as an efficient catalyst for click synthesis of tetrazoles

In this study, we have prepared a novel bis-Schiff-base copper(ii) complex by modifying Fe3O4 with acetylacetone functionalities and subsequently forming a Schiff base with 2-picolylamine and CuCl2 through a template method. Immobilization of 2,4-pentanedione and its reaction with 2-picolylamine enabled the synthesis of 1,3-diketimines (HNacNac) as an anionic ligand. This unique design resulted in a tetradentate N4 coordination sphere for copper(ii) ion complexation. The resulting heterogeneous catalyst, [Fe3O4@Sil-Schiff-base-Cu(ii)], efficiently catalyzed the click condensation of diverse aryl nitriles with sodium azide to produce 5-substituted 1H-tetrazoles in high yields and selectivity. The catalyst demonstrated remarkable stability and recyclability without appreciable loss of catalytic activity, as confirmed by hot filtration and reusability studies.

Diversely functionalized isoquinolines and their core-embedded heterocyclic frameworks: a privileged scaffold for medicinal chemistry

Isoquinoline-enrooted organic small-molecules represent a challenging molecular target in the organic synthesis arsenal attributed to their structural diversity and therapeutic importance. Into the bargain, isoquinolines are significant structural frameworks in modern medicinal chemistry and drug development. Consequently, synthetic organic and medicinal chemists have been intensely interested in efficient synthetic tactics for the sustainable construction of isoquinoline frameworks and their derivatives in enantiopure or racemic forms. This review accentuates an overview of the literature on the modern synthetic approaches exploited in synthesising isoquinolines and their core embedded heterocyclic skeletons from 2021 to 2022. In detail, the methodologies and inspected pharmacological studies for the array of diversely functionalized isoquinolines or their core-embedded heterocyclic/carbocyclic structures involving the introduction of substituents at C-1, C-3, and C-4 carbon and N-2 atom, bond constructions at the C1-N2 atom and C3-N2 atom, and structural scaffolding within isoquinoline compounds have been reviewed. This intensive study highlights the need for and relevance of relatively unexplored bioisosterism employing isoquinoline-based small-molecules in drug design.

Mukaiyama aldol reaction: an effective asymmetric approach to access chiral natural products and their derivatives/analogues

The Mukaiyama aldol reaction is generally a Lewis-acid catalyzed cross-aldol reaction between an aldehyde or ketone and silyl enol ether. It was first described by Mukaiyama in 1973, almost 5 decades ago, to achieve the enantioselective synthesis of β-hydroxy carbonyl compounds in high percentage yields. Mukaiyama aldol adducts play a pivotal role in the synthesis of various naturally occurring and medicinally important organic compounds such as polyketides, alkaloids, macrolides, etc. This review highlights the significance of the Mukaiyama aldol reaction towards the asymmetric synthesis of a wide range of biologically active natural products reported recently (since 2020).