Transition metal-free coupling of terminal alkynes and hypervalent iodine-based alkyne-transfer reagents to access unsymmetrical 1,3-diynes

Recent progress in alkynylation with hypervalent iodine reagents

Although alkynes are one of the smallest functional groups, they are among the most versatile building blocks for organic chemistry, with applications ranging from biochemistry to material sciences. Alkynylation reactions have traditionally relied on the use of acetylenes as nucleophiles. The discovery and development of ethynyl hypervalent iodine reagents have allowed to greatly expand the transfer of alkynes as electrophilic synthons. In this feature article the progress in the field since 2018 will be presented. After a short introduction on alkynylation reactions and hypervalent iodine reagents, the developments in the synthesis of alkynyl hypervalent iodine reagents will be discussed. Their recent use in base-mediated and transition-metal catalyzed alkynylations will be described. Progress in radical-based alkynylations and atom-economical transformations will then be presented.

Iron-Catalyzed Cadiot-Chodkiewicz Coupling with High Selectivity in Water under Air

An iron-based catalytic system was developed for the cross-coupling of 1-bromoalkynes with terminal alkynes to selectively generate unsymmetrical 1,3-butadiynes in water under air. It was found that a combination of 1-bromoalkynes derived from less acidic terminal alkynes with more acidic counterparts would greatly enhance yields and selectivity for unsymmetrical 1,3-butadiynes. The reaction was also applicable for the synthesis of unsymmetrical 1,3,5-hexatriynes through coupling of 1-bromoalkynes and trimethylsilyl-protected 1,3-butadiynes in a one-pot manner.

Highly selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes

A highly efficient method for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes via selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums using the Pd(OAc)2-DPPE and Pd2(dba)3-TFP complexes as catalysts, respectively, has been successfully developed. Though the alkyl substituted conjugated enediynes and unsymmetrical 1,3-diynes were not obtained, this case is also remarkable as the same starting materials could selectively produce either aryl substituted conjugated enediynes or unsymmetrical 1,3-diynes in moderate to excellent yields (up to 99%) in the different Pd-phosphine catalytic systems.

Asymmetric catalytic alkynylation of thiazolones and azlactones for synthesis of quaternary α-amino acid precursors

Asymmetric alkynylation of thiazolones and azlactones with alkynylbenziodoxolones as the electrophilic alkyne source catalyzed by thiourea phosphonium salt is described. By using thiazolones as nucleophiles, the desired alkyne functionalized thiazolones were obtained in 55-89% yields with 31-86% ee. Azlactones gave the desired products in comparable yields with lower enantioselectivities. Ring-opening of the alkynylation products led to α,α-disubstituted α-amino acid derivatives efficiently without loss of enantioselectivity.

Synthesis, Characterization of Spirocyclic λ3 -Iodanes and Their Application to Prepare 4,1-Benzoxazepine-2,5-diones and 1,3-Diynes

Herein, a [3+2] cycloaddition of aza-oxyallylic cations with ethynylbenziodoxolones for synthesis of new λ³ -iodanes containing spirocyclic 4-oxazolidinone has been developed. This cyclic λ³ -iodanes display stability in air and excellent solubility in organic solvent. Using them as substrate, both the 4,1-benzoxazepine-2,5-diones and symmetrical 1,3-diynes derivatives were afforded in high yield under copper(I)-catalyzed conditions.