Diazodiphenylmethane and Monosubstituted Butadienes: Kinetics and a New Chapter of Vinylcyclopropane Chemistry

Abstract

Dedicated to Emanuel Vogel, the discoverer of the vinylcyclopropane rearrangement, on the occasion of his 80th birthday Diazodiphenylmethane (DDM) undergoes cycloadditions to 1-substituted buta-1,3-dienes exclusively at the C(3)¼C(4) bond. At room temperature, the N 2 loss from the initially formed 4,5-dihydro-3H-pyrazoles 2 is faster than the cycloaddition and furnishes the vinylcyclopropane derivatives 7 and 9 with structural retention at the C(1)¼C(2) bond. 2-Substituted butadienes react with DDM at the C(3)¼C(4) bond to give 12; isoprene, however, affords 3,4/1,2 products in the ratio of 86 : 14. DDM is a nucleophilic 1,3-dipole: 1-Cyanobutadiene reacts 400 times faster than 1-methoxybuta-1,3-diene (DMF, 408). The log k 2 for the additions to six 1-substituted butadienes show a linear correlation with s p (Hammett) and r ¼ þ 2.9; the log k 2 of five 2-substituted butadienes are linearly related to Tafts s I (r ¼ þ 1.7). The structures of the vinylcyclopropanes 7, 9, and 12 are established by NMR spectra and oxidation. A cyclopropyl carbinyl cation is made responsible for the isomerization of 12, R ¼ Ph, Me, by acetic acid to 4-substituted 1,1-diphenylpenta-1,3-dienes 25 and 29; TsOH at 2008 converts 25 further to 9,10-dihydro-9-methyl-10-phenyl-9,10-ethanoanthracene (27). Thermal rearrangement of 7, 9, and 12 at 200 -3008 produces the 3-or 1-substituted 4,4-diphenylcyclopentenes 30 and 31. These give the same mass spectra as the vinylcyclopropanes, and an open-chain distonic radical cation is suggested as common intermediate. Besides spectroscopic evidence for the cyclopentene structures, hydrogenation and epoxidation are described; NMR data support the trans-attack by perbenzoic acid.

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

“…New Contributions. As described in a preceding paper, 1-(2-arylethenyl)-2,2-diphenylcyclopropanes became easily accessible [18]. It was shown that three Ph groups indeed stabilize the TS and bring down the temperature of the vinylcyclopropane rearrangement.…”

“…It was suggested in the preceding paper [18] that the radical cations of 22 and 23 furnish one and the same open-chain 24 (Scheme 5). This Table 5.…”

“…The ring enlargement of the parent compound (E)-22a was described in the preceding paper, and 23a was characterized by epoxidation to give 25 and by catalytic hydrogenation [18].…”

“…Recently, we described the preparation of vinylcyclopropane derivatives 8 by the interaction of diazo(diphenyl)methane with 1-substituted buta-1,3-dienes [18] (Scheme 3). The 1,3-cycloaddition to the unsubstituted C¼C bond of 6 at room temperature is followed by a fast elimination of N 2 from the initially formed 4,5-dihydro-3H-pyrazole 7; the (E)-configuration at the disubstituted C¼C bond of 6 is retained.…”

“…Anthracene-9-aldehyde (17) was subjected to a modified LeuckartÀWallach reaction to give 9-[(dimethylamino)methyl]-anthracene (18). The quaternary ammonium salt 19, obtained with MeI, was converted to the phosphonium iodide 20 with Ph 3 P in refluxing BuOH (72% for 17 !…”