Dimerization of cycloproparenes by silver ion

Aryl-substituted methylidenecyclopropa[b]naphthalenes: synthesis and attempted silver(I)-mediated dimerization

“…Rather, the first derivatives were subjected to silver(I) in methanol in a study 23 that predates the dimerization work of Billups. [15][16][17][18] To date this gap has not been bridged. Thus complexation of, e.g.…”

“…In this case the reaction provided a separable 3:1 mixture of 1-(2-naphthyl)-2-phenylethyne (15) 23 and 1-(2-naphthyl)-2-phenylethanone (17) 23 in 83% combined yield, along with unchanged substrate 1 (15%) (Scheme 4). Alkyne 15 has been isolated previously from 1, but in only 31% yield, by reaction with Ag(I) in tert-butanol where relief of ring strain by proton transfer is facilitated by the metal ion; 23 the size and nucleophilicity of the tert-butyl group does not allow for capture to give enol but does provide for a more complex product mixture.…”

“…That the reaction conditions employed herein are appropriate for dimerization has been confirmed from successful dimerization of 3 to 6,13-dihydropentacene in 73% yield. 15,17 The steric constraints present at C1 of the exocyclic alkenes 1-5 (and disilane 4) are too large to allow dimerization as only products of ring opening (or unchanged starting material) are recorded .…”

“…4 The Ag(I)-mediated opening is particularly efficacious, as illustrated by its use in the characterization of 1H-cyclopropa [b]naphthalene-3,6-dione, 14 but it is its application to the dimerization of the cycloproparenes that has commanded much recent attention. [15][16][17][18] For the simple cycloproparenes, the dimerization reaction entails the dropwise addition of an anhydrous chloroform solution of the cycloproparene to a suspension of AgBF 4 (ca. 1 mol %) in the same solvent at 0 o C. 15 Such reactions are usually complete within a few minutes and, as the anhydrous non-nucleophilic solvent cannot intercept the σ complex, a second equivalent of cycloproparene binds with the ring-opened cation ultimately to yield cycloproparene dimer (Scheme 1).…”

“…[15][16][17][18] For the simple cycloproparenes, the dimerization reaction entails the dropwise addition of an anhydrous chloroform solution of the cycloproparene to a suspension of AgBF 4 (ca. 1 mol %) in the same solvent at 0 o C. 15 Such reactions are usually complete within a few minutes and, as the anhydrous non-nucleophilic solvent cannot intercept the σ complex, a second equivalent of cycloproparene binds with the ring-opened cation ultimately to yield cycloproparene dimer (Scheme 1). Of the two possible products of dimerization the linear isomer dominates, as dictated by addition of the Ag(I)-complexed cycloproparene to the second molecule of reactant, and it is usually present in excellent yield as illustrated by the 90% conversion of cyclopropabenzene into 9,10-dihydroanthracene (Scheme 1 …”