Base‐Promoted Tandem Reaction Involving Insertion into Carbon–Carbon σ‐Bonds: Synthesis of Xanthone and Chromone Derivatives

Tandem reactions using base‐promoted processes have been developed for the synthesis of xanthone and chromone derivatives. The first examples of base‐promoted insertion reactions of isolated carbon–carbon triple bonds into carbon–carbon σ‐bonds have been reported. Using these approaches, polycyclic structures can be prepared. This reaction has the potential to become a general synthetic protocol for the preparation of multi‐substituted xanthones and chromones due to the abundance of easily accessible starting materials possessing diverse substituent groups.     

A Facile Synthesis of Novel Cyclic Esters of γ‐Keto Acid Derivatives by Heck Coupling Reaction

γ‐Keto acids and esters are highly useful compounds in organic synthesis, because a number of five‐membered carbocycles and various other heterocycles can be readily obtained from them. A number of γ‐keto acids derivatives have been synthesized with high yield by Heck coupling reaction with different alkenes using Pd(OAc)₂ as catalyst in dioxane solvent. The obtained products were characterized by elemental analysis, IR, proton NMR, and mass spectral studies.     

Insertion of Isolated Alkynes into Carbon–Carbon σ‐Bonds of Unstrained Cyclic β‐Ketoesters via Transition‐Metal‐Free Tandem Reactions: Synthesis of Medium‐Sized Ring Compounds

The transition‐metal‐free insertion of isolated alkynes into carbon–carbon σ‐bonds of unstrained cyclic β‐dicarbonyl compounds has been reported. These tandem reactions offer an efficient synthesis of medium‐sized ring or fused‐ring compounds through ring expansion. The methodology has the potential to be widely used throughout organic synthesis due to the easily accessible starting materials and mild reaction conditions.     

Synthesis of α‐Fluoroketones by Insertion of HF into a Gold Carbene

Reported is an efficient synthesis of α‐fluoroketones by insertion of hydrogen fluoride (HF) into the gold carbene intermediate, generated from a cationic gold catalyzed addition of N‐oxides to alkynes. This method results in excellent chemical yields for a wide range of alkyne substrates and demonstrates good functional‐group tolerance.