Gold(I)-Mediated Cycloisomerization/Cycloaddition Enables Bioinspired Syntheses of Neonectrolides B-E and Analogues

o-Quinone methides in natural product synthesis: an update

In recent years, ortho-quinone methides have emerged as indispensable reactive species for enhancing synthetic efficiency in accessing various bioactive natural products. Importantly, the emulation of nature's patterns and strategies has yielded numerous refined synthetic pathways for the construction of intricate molecules. o-Quinone methides (o-QMs) have demonstrated remarkable versatility in organic synthesis, especially in strategies guided by biomimetic logic. This review aims to delve into bio-inspired strategies employed over the past five years in the total synthesis of natural products involving ortho-quinone methides.

Iridium-catalyzed tandem olefination/aza-Michael reaction: rapid access to N-N functionalized hydrazides

An Ir-catalyzed tandem olefination/aza-Michael reaction of protected benzoylhydrazine derivatives with olefins under mild conditions has been developed. This method can be successfully applied to the construction of various structurally N-N-functionalized hydrazide derivatives bearing the α,β-unsaturated side chain in good to excellent yields. In particular, the deaminoprotected products can be used as potential precursors for the construction of N-N axially chiral compounds.

Gold-catalyzed cyclization and cycloaddition in natural product synthesis

Covering: 2016 to mid 2023Transition metal catalysis, known for its remarkable capacity to expedite the assembly of molecular complexity from readily available starting materials in a single operation, occupies a central position in contemporary chemical synthesis. Within this landscape, gold-catalyzed reactions present a novel and versatile paradigm, offering robust frameworks for accessing diverse structural motifs. In this review, we highlighted a curated selection of publications in the past 8 years, focusing on the deployment of homogeneous gold catalysis in the ring-forming step for the total synthesis of natural products. These investigations are categorized based on the specific ring formations they engender, accentuating the prevailing gold-catalyzed methodologies applied to surmount intricate challenges in natural products synthesis.

Natural product anticipation through synthesis

Natural product synthesis remains one of the most vibrant and intellectually rewarding areas of chemistry, although the justifications for pursuing it have evolved over time. In the early years, the emphasis lay on structure elucidation and confirmation through synthesis, as exemplified by celebrated studies on cocaine, morphine, strychnine and chlorophyll. This was followed by a phase where the sheer demonstration that highly complex molecules could be recreated in the laboratory in a rational manner was enough to justify the economic expense and intellectual agonies of a synthesis. Since then, syntheses of natural products have served as platforms for the demonstration of elegant strategies, for inventing new methodology 'on the fly' or to demonstrate the usefulness and scope of methods established with simpler molecules. We now add another aspect that we find fascinating, viz. 'natural product anticipation'. In this Review, we survey cases where the synthesis of a compound in the laboratory has preceded its isolation from nature. The focus of our Review lies on examples where this anticipation of a natural product has triggered a successful search or where synthesis and isolation have occurred independently. Finally, we highlight cases where a potential natural product structure has been suggested as a result of synthetic endeavours but not yet confirmed by isolation, inviting further collaborations between synthetic and natural product chemists.

Biomimetic approach to the catalytic enantioselective synthesis of tetracyclic isochroman

Polyketide oligomers containing the structure of tetracyclic isochroman comprise a large class of natural products with diverse activity. However, a general and stereoselective method towards the rapid construction of this structure remains challenging due to the inherent instability and complex stereochemistry of polyketide. By mimicking the biosynthetic pathway of this structurally diverse set of natural products, we herein develop an asymmetric hetero-Diels–Alder reaction of in-situ generated isochromene and ortho-quinonemethide. A broad range of tetracyclic isochroman frameworks are prepared in good yields and excellent stereoinduction (up to 95% ee) from readily available α-propargyl benzyl alcohols and 2-(hydroxylmethyl) phenols under mild conditions. This direct enantioselective cascade reaction is achieved by a Au(I)/chiral Sc(III) bimetallic catalytic system. Experimental studies indicate that the key hetero-Diels-Alder reaction involves a stepwise pathway, and the steric hindrance between in-situ generated isochromene and t-Bu group of Sc(III)/N,N’-dioxide complex is responsible for the enantioselectivity in the hetero-Diels–Alder reaction step.

General and stereoselective synthesis of tetracyclic isochroman-containing polyketide oligomers is challenging. Here, the authors report on an Au(I)/chiral Sc(III) bimetallic catalyst for a biomimetic asymmetric hetero-Diels–Alder reaction for in-situ generation of isochromene and ortho-quinonemethide.