Lewis Acid Catalyzed Reaction of Arylvinylidenecyclopropanes with Ethyl (Arylimino)acetates:  A Facile Synthetic Protocol for Pyrrolidine and 1,2,3,4-Tetrahydroquinoline Derivatives

Abstract

[reaction: see text] A number of pyrrolidine and 1,2,3,4-tetrahydroquinoline derivatives are prepared selectively in moderate to good yields by the reaction of arylvinylidenecyclopropanes 1 with ethyl (arylimino)acetates 2 in the presence of Lewis acid depending on the electronic nature both of 2 and R1 or R2 aromatic groups of 1.

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). 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).…”

“…The reaction conditions have been carefully examined in a similar way ( Table 3). The examination of Lewis acids and solvent effects revealed that ScA C H T U N G T R E N N U N G (OTf) 3 is the best catalyst in the reaction of 1 k with 2 b and DCE is the solvent of choice (Table 3, entries 1-15). Examination of the reaction temperature also indicated that this reaction should Table 2.…”

“…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.…”

“…[1] It is known that VDCPs can undergo a variety of ring-openingcycloaddition reactions upon heating or photoirradiation and by using Lewis acids as the catalysts because the relief of ring strain can provide a powerful thermodynamic driving force. [2,3] Thus far, a number of interesting skeletal conversions of VDCPs have been explored. For example, we have recently reported an interesting Lewis acid catalyzed intramolecular rearrangement of diarylvinylidenecyclopropanes containing one, two, or three substituents at the 1-and/or 2-position of the corresponding cyclopropane, which gave 6aH-benzo [c]fluorine derivatives in a double-intramolecular Friedel-Crafts reaction or indene or naphthalene derivatives via an intramolecular Friedel-Crafts reaction (Scheme 2).…”

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

“…[118] The authors have proposed a plausible mechanism for the formation of these 1,2,3,4-tetrahydroquinolines 216a-g which is outlined in Scheme 72. First, ethyl(arylimino)acetate 215 activated by the Lewis acid is attacked by the central carbon of 214 to give the corresponding allylic carbocationic intermediate pair 217, 218.…”