Pauson-Khand Reaction of Allenic Hydrocarbons: Synthesis of 4-Alkylidenecyclopentenones

Acetylene and Ethylene: Universal C2 Molecular Units in Cycloaddition Reactions

Acetylene and ethylene are the smallest molecules that contain an unsaturated carbon–carbon bond and can be efficiently utilized in a large variety of cycloaddition reactions. In this review, we summarize the application of these C2 molecular units in cycloaddition chemistry and highlight their amazing synthetic opportunities.

1 Introduction

2 Fundamental Features and Differences of Cycloaddition Reactions Involving Acetylene and Ethylene

3 (2+1) Cycloaddition

4 [2+2] Cycloaddition

5 (3+2) Cycloaddition

6 [4+2] Cycloaddition

7 (2+2+1) Cycloaddition

8 [2+2+2] Cycloaddition

9 The Use of Acetylene and Ethylene Cycloaddition for Deuterium and 13C Labeling

10 Conclusions

Copper(I)-Catalyzed Kinetic Resolution of exo-3-Oxodicyclopentadienes and endo-3-Oxodicyclopentadiene

The first example of highly efficient kinetic resolution of exo-3-oxodicyclopentadienes and endo-3-oxodicyclopentadiene has been developed by means of Cu(I)-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylide. Compared with the existing methodologies for those synthetically important optically active convex molecules, the current protocol provides an alternative but more practical approach from the readily available racemic starting materials, which is free from the repetitive reduction/oxidation steps in the enzymatic resolution or the indispensable stoichiometric amount of chirality-induction reagents.

Recent Advances in the Pauson-Khand Reaction

The Pauson-Khand [2+2+1] cycloaddition of alkynes, alkenes, and carbon monoxide has been a vibrant area of research for more than 40 years. This review highlights recent achievements in the Pauson-Khand reaction, particularly in catalytic and asymmetric variants. Discussion of regioselectivity and advances in substrate scope is also presented.

Rh(I)-catalyzed Pauson-Khand-type cycloaddition reaction of ene-vinylidenecyclopropanes with carbon monoxide (CO)

An intramolecular Pauson-Khand type cycloaddition reaction of ene-vinylidenecyclopropanes with carbon monoxide has been established by using [Rh(COD)Cl](2) as the catalyst. The reaction was found to be highly efficient in solvents of 1,2-dichloroethane and 1,1,2,2-tetrachloroethane to give excellent yields of 90-99%. The reaction provides easy access to a series of fused 6,5-ring structures containing spiro-cyclopropane units that are useful for drug design and development. A mechanism of this cycloaddition process has been proposed accounting for structures of resulting products that were unambiguously assigned by X-ray diffractional analysis.