Gold-Catalyzed Synthesis of Diaza-hexatrienes Via Diazo Attack at Vinylgold Carbenes: An Easy Access to 1H-Pyrazolo[4,3-b]pyridine-5-ones

Light-Induced Metal-Free Generation of Cyanocarbenes from Alkynyl Triazenes for the Synthesis of Nitrile Derivatives

The chemistry of alkynyl triazenes is an emerging field for organic chemists and especially acid-induced nucleophilic functionalizations, either directly, or after a prior reaction towards aromatic triazenes under extrusion of nitrogen, paved the way for fruitful strategies. In contrast, the chemical behavior of alkynyl triazenes upon irradiation with light is still unknown. Herein we present the first photoactivation of alkynyl triazenes that triggers an uncommon reactivity pattern involving the cleavage of the N1-N2 bond of the triazene moiety resulting in a unique approach to cyanocarbenes from a readily available, stable, and insensitive precursor. This allows to access various nitrile compounds without the use of a toxic cyanating agent by exploiting the reactivity pattern of carbenes. By variation of the reaction conditions and light sources, different substitution patterns can be obtained selectively in good yields under mild and metal-free conditions, thus introducing the alkynyl triazene unit as a photo accessible methylene nitrile synthon. Using this synthon, subclasses like α-alkoxynitriles, α-aminonitriles and α-cyanohydrazones become easily available. These exhibit synthetically valuable substitution patterns for the synthesis of pharmaceuticals, intermediates for total synthesis and amino acid synthesis.

Catalyst-free diazo cross-coupling to access useful 3(2H)-furanone derivatives

Catalyst-free synthesis of 3(2H)-furanone derivatives has been achieved from metal-free cross-coupling of α-diazo ester and α-aryldiazo ketones. This reaction sequence comprises a prior Wolff rearrangement of α-aryldiazo ketones to 2-arylketenes, which are trapped in situ with α-diazo esters to form cyclopropanones before undergoing oxa-Nazarov cyclization.

Highly Site-Selective Oxidative Cyclization of Ene-ynamides via Non-Noble-Metal Catalysis: Access to Functionalized Lactams

Herein, an unprecedented non-noble-metal-catalyzed oxidation/cyclization of ene-ynamides is developed, allowing the synthesis of diversely functionalized lactams in moderate to good yields with excellent diastereoselectivities without the observation of typical cyclopropanation products. In combination with Ellman's tert-butylsulfinimine chemistry, chiral γ-lactams containing three contiguous stereocenters are obtained with high diastereo- and enantioselectivity. Moreover, density functional theory (DFT) calculations indicate that this protocol probably undergoes a carbon cation or proton transfer process.

Rhodium-Catalyzed Dearomative Rearrangement of 2-Oxypyridines with Cyclopropenes: Access to N-Alkylated 2-Pyridones

A rhodium-catalyzed dearomative O-to-N rearrangement reaction of 2-oxypyridines has been developed by using cyclopropenes as the carbene precursors. This protocol features broad substrate scope and mild reaction conditions, providing a...

Asymmetric [3 + 1]-Cycloaddition Reaction via Diazo Discrimination

The enantioselective [3 + 1]-cycloaddition of two structurally different diazo compounds has been achieved using chiral bisoxazoline copper(I) complexes as a catalyst, providing a novel route for the synthesis of cyclobutenes containing a quaternary stereocenter. Typically, this reaction represents the first example of asymmetric cross-electrophile coupling of two diazo substrates via carbene discrimination.