[2+2]-cycloadditions of alkenes with the triphenylallenyl cation

Lewis Acid Catalyzed Cascade Reactions of Diarylvinylidenecyclopropanes and 1,1,3‐Triarylprop‐2‐yn‐1‐ols or Their Methyl Ethers

“…We found that the reaction proceeded smoothly in 1,2-dichloroethane (DCE) to afford 2-benzhydrylidene-3,4,4,9-tetraphenyl-2,4-dihydro-1H-cyclopenta[b]naphthalene 3 a in 93 % yield within 6 h at À20 8C in the presence of ZrA C H T U N G T R E N N U N G (OTf) 4 (10 mol %, OTf = trifluoromethanesulfonate) ( 2 , and the Brønsted acid (TfOH) were not as effective as ZrA C H T U N G T R E N N U N G (OTf) 4 under the standard conditions ( Table 1, entries 1-6). When 2 b was used as a reactant, complex product mixtures were obtained at room temperature (20 8C) or even at 0 8C by using YbA C H T U N G T R E N N U N G (OTf) 3 or BF 3 ·OEt 2 as a Lewis acid in DCE (Table 1, entries 12-14).…”

“…When 2 b was used as a reactant, complex product mixtures were obtained at room temperature (20 8C) or even at 0 8C by using YbA C H T U N G T R E N N U N G (OTf) 3 or BF 3 ·OEt 2 as a Lewis acid in DCE (Table 1, entries 12-14). However, the Lewis acids BF 3 ·OEt 2 and Zr-A C H T U N G T R E N N U N G (OTf) 4 (10 mol %) produced 3 a in 78 and 85 % yields, respectively at À20 8C (Table 1, entries 15 and 16). Therefore, on the basis of the above results, the best reaction conditions for the formation of 3 were to carry out the reaction of VDCPs 1 with 2 a in DCE at À20 8C with ZrA C H T U N G T R E N N U N G (OTf) 4 (10 mol %) as a Lewis acid.…”

“…However, the Lewis acids BF 3 ·OEt 2 and Zr-A C H T U N G T R E N N U N G (OTf) 4 (10 mol %) produced 3 a in 78 and 85 % yields, respectively at À20 8C (Table 1, entries 15 and 16). Therefore, on the basis of the above results, the best reaction conditions for the formation of 3 were to carry out the reaction of VDCPs 1 with 2 a in DCE at À20 8C with ZrA C H T U N G T R E N N U N G (OTf) 4 (10 mol %) as a Lewis acid. …”

“…Examination of the reaction temperature also indicated that this reaction should Table 2. ZrA C H T U N G T R E N N U N G (OTf) 4 catalyzed reactions of VCPs with 1,1,3-triphenyl-prop-2-yn-1-ols. [a] Isolated yields.…”

“…General procedure for Lewis acid catalyzed reactions of arylvinylidenecyclopropanes with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers: Arylvinylidenecyclopropane 1 (0.2 mmol), 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers 2 (0.4 mmol) and ZrA C H T U N G T R E N N U N G (OTf) 4 or ScA C H T U N G T R E N N U N G (OTf) 3 (10 mol %) were added into a Schlenk tube under an argon atmosphere. The reaction mixture was stirred at À20 8C for 6 h in DCE, then the solvent was removed under reduced pressure and the residue was purified by flash column chromatography.…”