This review comprehensively summarizes the advances achieved in catalytic intermolecular annulations of ynamides from 2010 to 2020.

A strategy for achieving diastereodivergent azidations of enynes has been developed, employing azide transfer from the M-N3 complex to alkyl radicals. Following this concept, the diastereoselectivity has been switched by modulating the transition metals and the ligands. The Mn(III)-mediated radical cyclization/azidation cascade of 1,7-enynes afforded trans-fused pyrrolo[3,4-c]quinolinones, whereas the Cu(II)/bipyridine system gave cis-products.

An unprecedented TfNH-catalyzed formal [3 + 2] cycloaddition of ynamides with dioxazoles was developed to construct various polysubstituted 4-aminooxazoles. This approach features a metal-free catalytic bimolecular assembly of oxazole motifs, a low-cost catalyst, exceptionally mild reaction conditions, a very short reaction time, a broad substrate scope, and high efficiency. This metal-free protocol may find applications in pharmaceutical-oriented synthesis.

Several Cu(I) complexes of 2,2'-bipyridines were studied for the catalytic coupling of aryl iodides and phenols and 4,4'dimethoxy-2,2'-bipyridine was shown to be an effective ligand of CuI in 1:2 (CuI:ligand) ratio for the synthesis of a wide range of diaryl ethers (up to 97% yield) using K 3 PO 4 as base in DMF at 100°C. The catalysis was highly dependent on the reaction temperature and was successfully applied in the coupling with more attractive and challenging substrates, aryl bromides, at 140°C in good-to-excellent yields (78À 95%). Moreover, the heteroaromatic effect for the reaction was studied and gave a comparable result with phenyl group (up to 95% yield). Significantly, a structurally related N,N-bidentate ligand, 4,7dimethoxy-1,10-phenanthroline, exhibited better performance for less-reactive combinations of aryl halides and phenols.

2-Trifluoromethyl-5-(arylsulfonyl)methyl pyrroles and 2-trifluoromethyl-4-(arylsulfonyl)methyl pyrroles were selectively synthesized from trifluoromethyl-substituted 3-aza-1,5-enynes via a cyclization/sulfonyl group migration cascade catalyzed by AgOOCCF3 and CsOPiv, respectively. Alkylvinyl-substituted pyrroles were generated from seven-atom skeleton 3-aza-1,5-enynes via aryl sulfinic acid elimination in the presence of Cs2CO3. Two ion-pair intermediates were proposed and a key intermediate, aza-diene-yne, was successfully isolated in the mechanistic studies.

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A Brønsted acid-catalyzed formal [5+2+1] cycloaddition of ynamides and isoxazoles with water is described. This process provides atom-economical access to oxygen-bridged tetrahydro-1,4-oxazepines, where the bridged oxygen atom originates from water. The unique property of the Brønsted acid shows distinct chemoselectivity from the corresponding gold-catalyzed cycloadditions.

Oxadiazolones are first employed as the three-atom coupling partners in the TfNH-catalyzed cycloaddition with ynamides. This formal [3 + 2] cycloaddition allows a rapid synthesis of aminoimidazoles with a broad substrate scope. The approach also features a metal-free catalytic cycloaddition process, which may find applications in the synthesis of bioactive molecules. Besides, the resulting N-methyl products can further be readily converted to free N-H aminoimidazoles.