Construction of heterocyclic rings from cyclopropenes

Heterocyclic rings are the fundamental building blocks of biological systems and have wide applications in synthetic chemistry and medicinal science. The development of novel synthetic methodology for heterocyclic skeletons from a variety of starting materials has made great progress in the past decades. Meanwhile, highly strained cyclopropenes as reactive reagents in organic transformations have drawn much attention from chemists. The rich chemical reactivity and reaction routes have been well investigated, and some review articles related to the reactivity of cyclopropenes and the construction of carbocycles and acyclic compounds have appeared in these years. Thus, this review mainly focuses on the progress in the construction of heterocyclic rings starting from various cyclopropenes including the reactions of commonly available stable cyclopropenes, in situ generated reactive cyclopropenes and cyclopropene precursors during this decade. Firstly, the transformations of common cyclopropenes into donor-type vinyl metal carbenes via transition metal induced ring opening, direct metalation of the CC bond of metal complexes, and cycloaddition reactions with 1,3-dipoles are described. Next, the annulation reactions of reactive cyclopropenes generated in situ with donor-acceptor reagents, intramolecular nucleophilic addition, and the cycloaddition reactions with 1,3-dipoles are introduced. Then, the transformation of cyclopropene precursors such as alkyl 1-chloro- or 1-alkoxy-2-aroylcyclopropanecarboxylates into five-membered heteroaromatic compounds is also mentioned. In addition, a brief outlook of the opportunity and challenges in the field of bio-orthogonal reactions related to cyclopropenes is given.

Hetero-bimetallic cooperative catalysis for the synthesis of heteroarenes

Review covering the synthesis of 5- and 6-membered as well as condensed heteroarenes, focussing on the combinations in cooperative catalytic systems in strategies used to achieve selectivity and also highlights the mode of action for the cooperative catalysis leading to the synthesis of commercially and biologically relevant heteroarenes.

Insights into the mechanisms of Cu(i)-catalyzed heterocyclization of α-acyl-α-alkynyl ketene dithioacetals to form 3-cyanofurans: the roles of NH4OAc

NH₄OAc is decomposed into NH₃ and HOAc, and both NH₃ and HOAc as the proton shuttle can prompt catalytic reactions.

A calcium catalysed regioselective (5-exo dig) tandem process for the synthesis of fully substituted furans

An efficient and highly regioselective synthesis of fully substituted furans has been described using Ca(OTf)₂. The reaction proceeds through tandem alkylation, 5-exo dig cyclisation and isomerization under solvent free conditions.

Zn/Sc bimetallic relay catalysis: one pot cycloisomerization/carbonyl–ene reaction toward oxazole derivatives

A novel tandem metal relay catalytic system combining Zn(ii)-catalyzed cycloisomerization and a Sc(iii)-catalyzed carbonyl–ene reaction has been successfully developed.

Successive Cu/Pd transmetalation relay catalysis in stereoselective synthesis of tetraarylethenes

A new and efficient strategy for the synthesis of tetraaryl-substituted olefins with two cis furans based on a Cu/Pd catalyzed oxidative coupling reaction of cyclopropene with internal alkyne was developed. These novel tetraarylethenes were fully characterized and proved to be good AIE luminogens.

Tandem metal relay catalysis: from cyclopropene to polysubstituted furan

Transmetalation is a key step in traditional coupling reactions. An efficient synthetic methodology of tetrasubstituted furans from cyclopropenes with Cu–Pd transmetalation relay catalysis was presented.