Diverse Pathways in Catalytic Reactions of Propargyl Aryldiazoacetates: Selectivity between Three Reaction Sites

Rh(II)-Catalyzed Selective C(sp3)-H/C(sp2)-H Bonds Cascade Insertion to Construct [6-8-6] Benzo-Fused Scaffold

The fused eight-membered carbocycles (EMCs) play vital roles in the medicinal and biological investigations of many natural products and marketed drugs. The traditional synthesis of [6-8-6] benzo-fused derivatives involves multistep reactions and low yields, making the development of a one-step synthesis method a more challenging work. Here, we present a novel strategy for one-step construction of [6-8-6] benzo-fused scaffold from propargyl diazoacetates substituted with benzyl-nitrogen heterocyclic ring via Rh(ll)-catalyzed carbene/alkyne metathesis (CAM) and selective C-H bond insertion. This method exhibits a specific substrate scope, simple operation, mild reaction conditions, and high atom efficiency. Mechanistically, the process involves sequential CAM, 1,3-H-shift, intramolecular nucleophilic attack, and selective C(sp3)-H/C(sp2)-H bonds cascade insertion. Notably, the unique spirocyclic zwitterionic intermediate generated in this sequence contributes to N-heterocycle migration and fused eight-membered carbocycle formation. Additionally, the C(sp3)-H bond insertion connected to the oxygen atom rather than the nitrogen atom has been unexpectedly confirmed with the assistance of the spirocyclic zwitterionic intermediate. Overall, our findings open up a new avenue for the construction of [6-8-6] benzo-fused scaffold.

Visible-Light Photoredox Catalyzed Regioselective 1,4-Hydroalkylation of 1,3-Enyne

Described herein is a visible-light photoredox-catalyzed regioselective 1,4-hydroalkylation of 1,3-enynes. Various of di- and tri-substituent allenes were really accessible under the present reaction conditions. The visible-light photoredox activation of the carbon nucleophile to generate its radical species, allowing the addition with un-activated enynes. The synthetic utility for the present protocol was demonstrated by a large-scale reaction, as well as the derivatization of the allene product.

Recent Advances in Catalytic Alkyne Transformation via Copper Carbene Intermediates

As one of the abundant and inexpensive metals on the earth, copper has demonstrated broad applications in synthetic chemistry and catalysis. Among these copper-catalyzed advances, copper carbenes are versatile and reactive intermediates that can mediate a variety of transformations, which have attracted much attention in the past decades. The present review summarizes two different reaction models that take place between a copper carbene intermediate and alkyne species, including the cross-coupling reaction of copper carbene intermediate with terminal alkyne, and the addition of copper carbene intermediate onto the C-C triple bond. This article will cover the profile from 2010 to 2021 by placing emphasis on the detailed catalytic models and highlighting the synthetic applications offered by these practical and mild methods.

Cp*RuCl-Vinyl Carbenes: Two Faces and the Bifunctional Role in Catalytic Processes

Ruthenium vinyl carbenes derived from Cp/Cp*RuCl-based complexes (Cp=cyclopentadiene, Cp*=1,2,3,4,5-pentamethylcyclopentadiene) have been routinely invoked as key intermediates in tandem reactions involving a carbene/alkyne metathesis (CAM). A priori, these intermediates resemble the Grubbs-type family of catalysts, but they exhibit a completely different reactivity pattern that few, if any, other catalytic system can reproduce so far. The reactivity of these species with α-unsubstituted and α-substituted alkynals showcases the peculiarities of these intermediates. Although Z-vinyl dihydrooxazines are preferentially obtained with the former, Z-vinyl epoxypyrrolidines are obtained with the latter. A combination of spectroscopic and computational data now prove that a η³ -coordination mode of the ruthenium vinyl carbene and the presence of a Lewis basic chloride ligand give rise to two markedly different stereoelectronic faces, which are responsible for the unconventional reactivity of these species.

Catalytic carbene/alkyne metathesis (CAM): a versatile strategy for alkyne bifunctionalization

Metal carbene, as a reactive intermediate, has shown versatile applications in modern organic synthesis. One of the priorities in this area is exploration of stable carbene precursors with structural diversity. Catalytic carbene/alkyne metathesis (CAM) with readily available and stable materials, such as α-carbonyl diazo compounds, provides an effective approach for the in situ generation of vinyl carbene intermediates, which is difficult to directly access with other carbene precursors. Thus, novel cascade transformations involving the CAM process for the straightforward construction of polycyclic frameworks have been well documented. Challenges including side reaction control and asymmetric catalysis in this area need to be explored. This review will summarize the recent advances in this field and be divided by the type of the terminating carbene reactions.

Intramolecular cycloaddition/rearrangement cascade from gold(iii)-catalysed reactions of propargyl aryldiazoesters with cinnamyl imines

Surprising rearrangement of dihydroazepinyl aryldiazoacetates from a gold-catalysed [4+3]-cycloaddition to conjugated cycloheptene-1,4-dione-enamines.

Chemoselective Asymmetric Intramolecular Dearomatization of Phenols with α-Diazoacetamides Catalyzed by Silver Phosphate

We report asymmetric dearomatization of phenols using Ag carbenoids from α-diazoacetamides. The Ag catalyst promoted intramolecular dearomatization of phenols, whereas a Rh or Cu catalyst caused C-H insertion and a Büchner reaction. Studies indicated Ag carbenoids have a carbocation-like character, making their behavior and properties unique. Highly enantioselective transformations using Ag carbenoids have not been reported. We achieved a Ag carbenoid-mediated chemo- and highly enantioselective phenol dearomatization with substrate generality for the first time.

A serendipitous cascade of rhodium vinylcarbenoids with aminochalcones for the synthesis of functionalized quinolines

A convergent 5-step cascade approach for the stereoselective synthesis of functionalized quinolines.