Optically Active 2,3-AllenoatesviaPalladium-Catalyzed Carbonylation of Enantioenriched Propargylic Mesylates

Synthesis of Multisubstituted 2,3-Allenamides via Palladium-Catalyzed Carbonylation of Propargylic Esters

2,3-Allenamides are an important class of unsaturated group-substituted carbonyl compounds. A palladium-catalyzed aminocarbonylation of propargyl acetates with amines for the synthesized tri-/tetrasubstituted 2,3-allenamides has been developed. A broad range of tri-/tetrasubstituted 2,3-allenamides have been prepared from propargyl acetates in good to excellent yields. The reaction featured mild reaction conditions and good functional group tolerance. The applicability of this methodology was further highlighted by the late-stage modification of several natural products and pharmaceuticals.

Palladium-catalyzed enantioselective carbonylation reactions

Carbonylation, one of the most powerful approaches to the preparation of carbonylated compounds, has received significant attention from researchers active in various fields. Indeed, impressive progress has been made on this subject over the past few decades. Among the various types of carbonylation reactions, asymmetric carbonylation is a straightforward methodology for constructing chiral compounds. Although rhodium-catalyzed enantioselective hydroformylations have been discussed in several elegant reviews, a general review on palladium-catalyzed asymmetric carbonylations is still missing. In this review, we summarize and discuss recent achievements in palladium-catalyzed asymmetric carbonylation reactions. Notably, this review’s contents are categorized by reaction type.

Copper-Catalyzed Tandem Cross-Coupling and Alkynylogous Aldol Reaction: Access to Chiral Exocyclic α-Allenols

An enantioselective copper-catalyzed tandem cross-coupling/alkynylogous aldol reaction has been developed. The tetrasubstituted allenoates containing both central and axial chirality have been obtained in moderate to good yields and excellent enantio- and diastereoselectivity. Distinct from the previous use of Cu(I) salts, this protocol features the use of copper(II) salts as a catalytic precursor in this asymmetric cross-coupling reaction.

Construction of Axially Chiral Compounds via Central-to-Axial Chirality Conversion

Central-to-axial chirality conversion represents a fascinating class of chemical processes consisting of the destruction of stereogenic centers and the simultaneous installation of axial chiral elements, which provides efficient methods for the preparation of axially chiral compounds. Using the strategy, a wide range of axially chiral compounds, including biaryls, heterobiaryls, aromatic amides, allenes and vinyl arenes, have been synthesized with high efficiency and excellent enantioselectivity. In addition, central-to-axial chirality conversion strategy has been applied to the synthesis of natural products. The strategy has undoubtedly become and will continue to be a hot research topic in the field of asymmetric catalysis and synthesis. In this minireview, we selected some examples to introduce the developments and trends in the central-to-axial chirality conversion strategy up to April 2020.

Efficient synthesis of tetrasubstituted 2,3-allenoates and preliminary studies on bioactivities

A general and highly efficient straightforward protocol for the preparation of tetrasubstituted 2,3-allenoates through a palladium-catalyzed coupling reaction of 3-alkoxycarbonyl propargylic carbonates and boronic acids with commercially available tri(o-tolyl)phosphine as a ligand has been developed.

Catalytic transient leaving group for atom-economic synthesis of allenes from 2-alkynols

An atom economic approach from readily available propargylic alcohols to allenes, the first carboxylation of propargylic alcohols, has been established. Through the cooperative binary catalysis of Pd and a phosphoric acid, the reaction afforded multi-substituted allenoates with a broad scope tolerating useful functional groups. The synthetic potential of the obtained products has been demonstrated.

2,3-Allenoic acids via palladium-catalyzed carboxylation of propargylic alcohols

The first example of Pd-catalyzed carboxylation of propargylic alcohols in the presence of CO (1 atm) and water affording 2,3-allenoic acids has been developed.

Rapid Asymmetric Synthesis of Disubstituted Allenes by Coupling of Flow-Generated Diazo Compounds and Propargylated Amines

We report herein the asymmetric coupling of flow‐generated unstabilized diazo compounds and propargylated amine derivatives, using a new pyridinebis(imidazoline) ligand, a copper catalyst and base. The reaction proceeds rapidly, generating chiral allenes in 10–20 minutes with high enantioselectivity (89–98 % de/ee), moderate yields and a wide functional group tolerance.

Synthesis of 2,3-allenylamides utilizing [1,2]-phospha-Brook rearrangement and their application to gold-catalyzed cycloisomerization providing 2-aminofuran derivatives

An efficient synthetic method for 2,3-allenylamides having an oxygen functionality at the 2-position was newly developed by utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis.