Asymmetric cyclopropane synthesis currently requires bespoke strategies, methods, substrates, and reagents, even when targeting similar compounds. This approach slows down discovery and limits available chemical space. Introduced herein is a practical and versatile diazocompound and its performance in the first unified asymmetric synthesis of functionalized cyclopropanes. The redox‐active leaving group in this reagent enhances the reactivity and selectivity of geminal carbene transfer. This effect allowed the asymmetric cyclopropanation of various olefins, including unfunctionalized aliphatic alkenes, that enables the three‐step total synthesis of (−)‐dictyopterene A. This unified synthetic approach delivers high enantioselectivities that are independent of the stereoelectronic properties of the functional groups transferred. Our results demonstrate that orthogonally differentiated diazocompounds are viable and advantageous equivalents of single‐carbon chirons.
A Cinchona-derived squaramide catalyzes the reaction between hydroxyindoles and isatins leading to enantioenriched indoles substituted in the carbocyclic ring. The reaction proceeds efficiently with differently substituted isatins, yielding the desired products with excellent regioselectivity, good yields, and high enantiocontrol. Moreover, every position of the carbocyclic ring of the indole can be functionalized by using the appropriate starting hydroxyindole. The OH group was removed smoothly upon hydrogenolysis of the corresponding triflate.
A quinine-derived thiourea organocatalyst promoted the highly enantioselective addition of naphthols and activated phenols to ketimines derived from isatins. The reaction afforded chiral 3-amino-2-oxindoles with a quaternary stereocenter in high yields (up to 99%) with excellent enantioselectivity (up to 99% ee). To the best of our knowledge, this transformation is the first highly enantioselective addition of naphthols to ketimines.
The first general catalytic method for the, so far elusive, enantioselective Friedel−Crafts functionalization of indoles in the carbocyclic ring is presented. This transformation contrasts with the usual tendency of these heterocycles to react at the azole ring. For this purpose, the four regioisomeric hydroxy carbocyclic-substituted indoles were reacted with several isatinderived ketimines, using a Cinchona alkaloid-based squaramide, in a low 0.5−5 mol % catalyst loading, as a bifunctional catalyst. This methodology allows the functionalization of indoles in every position of the carbocyclic ring in a regio-and enantioselective fashion, by switching only the position of the hydroxy group in the starting material. Furthermore, several transformations were carried out, including the reductive elimination of the hydroxy group.
Gold(I) chloride complexes are stable, widespread precatalysts that generally require activation by halide abstraction to display useful catalytic activity. Chloride scavenging is typically performed in situ by using silver salts. This procedure, apart from mandating the use of an additional metal, often negatively impacts the reaction outcome, because Ag additives are not catalytically innocent (silver effect). Therefore, both the development of alternative chloride scavengers and the design of self-activating gold(I) chloride complexes endowed with special ligands have lately been the subject of intense research efforts. This review describes recent advances in the field of silver-free Au(I) catalysis employing gold(I) chloride complexes, with an emphasis on approaches emerged in the last decade.
Alkynylcyclopropanes
have found promising applications in both
organic synthesis and medicinal chemistry but remain rather underexplored
due to the challenges associated with their preparation. We describe
a convenient two-step methodology for the alkynylcyclopropanation
of alkenes, based on the rhodium(II)-catalyzed decarbenation of 7-alkynyl
cycloheptatrienes. The catalytic system employed circumvents a fundamental
problem associated with these substrates, which usually evolve via
6-endo-dig cyclization or ring-contraction pathways
under metal catalysis. This unique performance unlocks a rapid access
to a diverse library of alkynylcyclopropanes (including derivatives
of complex drug-like molecules), versatile intermediates that previously
required much lengthier synthetic approaches. Combining experiments
and DFT calculations, the complete mechanistic picture for the divergent
reactivity of alkynylcycloheptatrienes under metal catalysis has been
unveiled, rationalizing the unique selectivity displayed by rhodium(II)
complexes.
Pyrrolidines are important heterocyclic compounds with endless applications in organic synthesis, metal catalysis, and organocatalysis. Their potential as ligands for first-row transition-metal catalysts inspired a new method to access complex poly-heterocyclic pyrrolidines in one step from available materials. This fundamental step forward is based on the discovery of an essential organoaluminum promoter that engages unactivated and electron-rich olefins in intermolecular [3+2] cycloadditions.
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