Rhodium-Catalyzed Branched and Enantioselective Direct α-Allylic Alkylation of Simple Ketones with Alkynes

Synergistic Homogeneous Asymmetric Cu Catalysis with Pd Nanoparticle Catalysis in Stereoselective Coupling of Alkynes with Aldimine Esters

Understanding the nature of a transition-metal-catalyzed process, including catalyst evolution and the real active species, is rather challenging yet of great importance for the rational design and development of novel catalysts, and this is even more difficult for a bimetallic catalytic system. Pd(0)/carboxylic acid combined system-catalyzed allylic alkylation reaction of alkynes has been used as an atom-economical protocol for the synthesis of allylic products. However, the asymmetric version of this reaction is still rather limited, and the in-depth understanding of the nature of active Pd species is still elusive. Herein we report an enantioselective coupling between readily available aldimine esters and alkynes using a synergistic Cu/Pd catalyst system, affording a diverse set of α-quaternary allyl amino ester derivatives in good yields with excellent enantioselectivities. Mechanistic studies indicated that it is most likely a synergistic asymmetric molecular Cu catalysis with Pd nanoparticle catalysis. The Pd catalyst precursor is transformed to soluble Pd nanoparticles in situ, which are responsible for activating the alkyne to an electrophilic allylic Pd intermediate, while the chiral Cu complex of the aldimine ester enolate provides chiral induction and works in synergy with the Pd nanoparticles.

Asymmetric α-Allylation of Amino Acid Esters with Alkynes Enabled by Chiral Aldehyde/Palladium Combined Catalysis

A highly efficient, atom-economical α-allylation reaction of NH2-unprotected amino acid esters and alkynes is achieved by chiral aldehyde/palladium combined catalysis. A diverse range of α,α-disubstituted nonproteinogenic α-amino acid esters are produced in 31-92% yields and 84-97% ee values. The allylation products are utilized for the synthesis of drug molecule BMS561392 and other chiral molecules possessing complex structures. Mechanistic investigations reveal that this reaction proceeds via a chiral aldehyde-/palladium-mediated triple cascade catalytic cycle.

Construction of quaternary carbon centers by KOtBu-catalyzed α-homoallylic alkylation of lactams with 1,3-dienes

We report a KOtBu-catalyzed α-homoallylic alkylation of lactams with 1,3-dienes.

Direct access to spirocycles by Pd/WingPhos-catalyzed enantioselective cycloaddition of 1,3-enynes

Spirocycles play an important role in drug discovery and development. The direct, catalytic, and enantioselective synthesis of spirocycles from readily available starting materials and in an atom economic manner remains a highly sought-after task in organic synthesis. Herein, an enantioselective Pd-hydride-catalyzed cycloaddition method for the synthesis of spirocyclic compounds directly from two classes of commonly available starting materials, 1,3-enynes and cyclic carbon−hydrogen (C−H) bonds, is reported. The reactions employ a chiral Pd/WingPhos catalyst to both suppress the formation of bis-allenyl by-products and control the stereoselectivity. 1,3-Enynes are used as dielectrophilic four-carbon units in the cycloaddition reactions, which also enables an enyne substrate-directed enantioselectivity switch with good levels of stereocontrol. The present spirocycle synthesis tolerates a broad range of functional groups of 1,3-enyne substrates, including alcohols, esters, nitriles, halides, and olefins. A variety of diverse cyclic nucleophiles, including pharmaceutically important heterocycles and carbocycles, can be flexibly incorporated with spiro scaffolds.

Spirocycles are traditionally difficult structures to synthesize due to the congested nature of the central atom. Here the authors show a method to synthesize quaternary carbon spirocycles in one step from 1,3-enynes and pyrazolidine-type heterocycles, both relatively unactivated structures, proceeding via palladium catalysis.

Enantioselective Addition of α-Nitroesters to Alkynes

By using Rh-H catalysis, we couple α-nitroesters and alkynes to prepare α-amino-acid precursors. This atom-economical strategy generates two contiguous stereocenters, with high enantio- and diastereocontrol. In this transformation, the alkyne undergoes isomerization to generate a Rh^III -π-allyl electrophile, which is trapped by an α-nitroester nucleophile. A subsequent reduction with In powder transforms the allylic α-nitroesters to the corresponding α,α-disubstituted α-amino esters.

Rhodium-catalyzed regio- and enantioselective allylic alkylation of pyrazol-5-ones with alkynes

An atom-economical, regio- and enantioselective allylic alkylation of pyrazol-5-ones with alkynes was developed under rhodium catalysis.