Ligand-controlled gold-catalyzed cycloisomerization of 1,n-enyne esters toward synthesis of dihydronaphthalene

Abstract

We describe herein a gold-catalyzed rearrangement of propargyl esters followed by allene-ene cyclization to afford substituted bicyclic [4.4.0] dihydronaphthalene compounds. This method is also applied to vinylethers and vinylamines of 1,7-enyne esters to form dihydroquinoline and dihydrobenzopyran structures. The basis of this transformation is the ligand-controlled preferential activation of the alkene over the allene, affording the desired aromatic bicyclic structures in moderate to excellent yields.

Synthesis of benzothiophene and indole derivatives through metal-free propargyl–allene rearrangement and allyl migration

“…Allene-mediated cyclization reactions are advantageous due to the convenient preparation of starting materials instead of the use of unstable or reactive polyfunctionalized allene substrates [ 17 – 27 ]. Although transition metal (e.g., Au, Pd)-catalysed propargyl–allenyl isomerization and cyclization reactions have been established [ 28 – 29 ], such transformations promoted by a base to construct heterocycles are not well-documented [ 30 – 31 ]. Recently, our group explored the utilization of β-sulfonium carbanions for the preparation of thiophene derivatives [ 19 ].…”

Synthesis of 1,2,3-triazole ligands, their metal complexes, and applications in catalysis; Gold (I) catalyzed 1,n-enyne ester cycloisomerization reactions

“…To evaluate further the cycloisomerization reaction, we examined reactions of internal alkenes (Scheme 5, 18) and of disubstituted terminal alkenes (Scheme 5, 19). The starting materials (18)(19)(20)(21) were prepared and subjected to gold catalysts under the optimized conditions. Based on 1 H NMR spectroscopy, the reactions were sluggish and only approximately 5% of the desired products were observed.…”

“…A tentative mechanism for the gold(I) catalyzed cycloisomerization reaction of 1,n-enyne esters (n = the number of atoms between the alkene and alkyne) to form the aromatic bicyclic resulted with the nucleophilic attack of the C-Au bond on to the oxonium intermediate. 20 Scheme 6. Tentative mechanism for cyclization catalyzed by gold cation.…”

“…17 Thereafter the importance of the 1,2,3-triazoles has been continuously demonstrated in organic synthesis, 18 pharmaceutical sciences 19 and medicinal chemistry. 20 The Click reaction proceeds smoothly under mild conditions with high yields. It involves a dinuclear CuAAC mechanism shown in Figure 7.…”

“…3+2] annulation between readily available terminal alkynes and aromatic or alkenic carboxamides under the mild conditions in presence of the gold (I) shown in below Scheme 43 20. A key intermediate involved in the catalytic cycle is a tricoordinatedAu (I) complex which is rare in gold catalysis.…”