A Crystalline Ready-to-Use Form of Cyclopentadiene

Abstract

Cyclopentadiene (Cpd) is widely used as a starting material in organic and inorganic chemistry. In neat form, Cpd dimerizes, making it necessary to distill it prior to use to obtain fully reactive material. We have screened three different tetraphenyladamantane octaethers for their ability to act as encapsulating organic crystal (EnOC) hosts for Cpd. To this end, we also synthesized 1,3,5,7-tetrakis(3,5-dimethoxyphenyl)adamantane, a new octaether, dubbed iso-TDA. Only one of the octaethers was found to produce inclusion complexes with Cpd in the crystalline state. The encapsulated diene was stable for one month and showed full reactivity in a series of different synthetic transformations.

Key words

cycloadditions - cyclopentadiene - inclusion complexes - uptake and release - X-ray crystal structure

• References and Notes

• 1 Grachev AA. Klochkov AO. Shiryaev VI. Russ. J. Appl. Chem. 2012; 85: 629
• 2 Accessed at https://scifinder.cas.org/scifinder/view/scifinder/ scifinderExplore.jsf; search performed on 29.03.2018.
• 3 Schwenger A. Frey W. Richert C. Chem. Eur. J. 2015; 21: 8781
• 4 Schwenger A. Frey W. Richert C. Angew. Chem. Int. Ed. 2016; 55: 13706
• 5 Richert C. Alexandre P.-E. Schwenger A. Frey W. Chem. Eur. J. 2017; 23: 9018
• 6 Richert C. Krupp F. Synlett 2017; 28: 1763
• 7 Mal D. Ray S. Eur. J. Org. Chem. 2008; 3014
• 8 To KK. W. Wang X. Yu CW. Ho Y-P. Au-Yeung SC. F. Bioorg. Med. Chem. 2004; 12: 4565
• 9 Bartlett PD. Wu C. J. Org. Chem. 1984; 49: 1880
• 10 Michieletto I. Fabris F. De Lucchi O. Tetrahedron: Asymmetry 2000; 11: 2835
• 11 Mlostoń G. Grzelak P. Linden A. Heimgartner H. Chem. Heterocycl. Compd. 2017; 53: 518
• 12 Ramesh C. Nayak TK. Burai R. Dennis MK. Hathaway HJ. Sklar LA. Prossnitz ER. Arterburn JB. J. Med. Chem. 2010; 53: 1004
• 13 Reichert VR. Mathias LJ. Macromolecules 1994; 27: 7015
• 14 Jing L. Ma H. Fan P. Jia Z. Chem. Nat. Compd. 2017; 53: 248
• 15 Krupka J. Pet. Coal 2010; 52: 290
• 16 Moffett RB. Org. Synth., Coll. Vol. IV 1963; 32: 41
• 17 Compound 6 Samples of [Cpd]_TDA (7, 20 mg, corresponding to 0.027 mmol Cpd) and p-benzochinone (5, 3.2 mg, 0.029 mmol) were dissolved in CHCl₃ (0.1 mL). The solution was stirred for 2 h at 22 °C. After removing the solvent under reduced pressure, the resulting crude product was purified by column chromatography (silica, CH₂Cl₂/PE 7:1, v/v, R_f = 0.27). The title compound was isolated as a yellowish solid (3.5 mg, 0.020 mmol, 74%) and 18 mg, 0.026 mmol TDA (90%) was recovered by eluting with the above mentioned solvent mixture. Compound 18 A sample of 6-bromopiperonal (16, 4.27 mg, 0.019 mmol), p-iodoaniline (17, 4.04 mg, 0.019 mmol) and encapsulated cyclopentadiene (7, 75 mg, corresponding to 0.095 mmol Cpd) were dissolved in CHCl₃ (0.2 mL). Then, Sc(OTf)₃ (0.91 mg, 0.0018 mmol) was dissolved in dry MeCN (0.04 mL). This solution was slowly added to the reaction mixture. The mixture was stirred for 5 h at 22 °C. After removing the solvent in vacuo, the resulting crude was purified via column chromatography (silica, PE/CH₂Cl₂ 1:4, v/v, R_f = 0.8). Compound 18 was isolated as an off-white solid (8.4 mg, 0.0175 mmol, 89%) and 72 mg, 0.11 mmol TDA (96%) was recovered by eluting with the above-mentioned solvent mixture. The analytical data were in accordance with the literature.^7,12