Studies on Synthesis of Polycyclic Aromatic Hydrocarbons Based on Difluorocarbocation Generation

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17. For our publications on the synthesis based on stabilized CF2 cations, see: (a) Ichikawa, J.; Jyono, H.; Kudo, T.; Fujiwara, M.; Yokota, M. Synthesis 2005, 2005, 39. (b) Ichikawa, J.; Kaneko, M.; Yokota, M.; Itonaga, M.; Yokoyama, T. Org. Lett. 2006, 8, 3167. (c) Yokota, M.; Fujita, D.; Ichikawa, J. Org. Lett. 2007, 9, 4639. (d) Fuchibe, K.; Takayama, R.; Yokoyama, T.; Ichikawa, J. Chem. Eur. J. 2017, 23, 2831. (e) Fuchibe, K.; Hatta, H.; Oh, K.; Oki, R.; Ichikawa, J. Angew. Chem. Int. Ed. 2017, 56, 5890. (f) Fuchibe, K.; Oki, R.; Hatta, H.; Ichikawa, J. Chem. Eur. J. 2018, 24, 17932.

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4. For our publications on the synthesis based on stabilized CF2 cations, see: (a) Ichikawa, J.; Jyono, H.; Kudo, T.; Fujiwara, M.; Yokota, M. Synthesis 2005, 2005, 39. (b) Ichikawa, J.; Kaneko, M.; Yokota, M.; Itonaga, M.; Yokoyama, T. Org. Lett. 2006, 8, 3167. (c) Yokota, M.; Fujita, D.; Ichikawa, J. Org. Lett. 2007, 9, 4639. (d) Fuchibe, K.; Takayama, R.; Yokoyama, T.; Ichikawa, J. Chem. Eur. J. 2017, 23, 2831. (e) Fuchibe, K.; Hatta, H.; Oh, K.; Oki, R.; Ichikawa, J. Angew. Chem. Int. Ed. 2017, 56, 5890. (f) Fuchibe, K.; Oki, R.; Hatta, H.; Ichikawa, J. Chem. Eur. J. 2018, 24, 17932. See also ref 1.

5. For our dehydrative PAH synthesis conducted in HFIP via fluorine-free carbocations, see: (a) Takahashi, I.; Hayashi, M.; Fujita, T.; Ichikawa, J. Chem. Lett. 2017, 46, 392. (b) Fujita, T.; Takahashi, I.; Hayashi, M.; Wang, J.; Fuchibe, K. Ichikawa, J. Eur. J. Org. Chem. 2017, 2017, 262.

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12. Throughout the studeis of Table 2-4, sideproducts such as regioisomers and overreaction products were not isolated.

13. The use of DDQ as a dehydrogenating agent resulted in low product yields.

14. The structures of PAHs 3g and 9h were confirmed by single crystal X-ray analysis.

3-8. References

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13. For C–C bond formation of 1,1-difluoroallenes at the position α to the fluorine substituents, see also: Mae, M.; Hong, J. A.; Xu, B.; Hammond, G. B. Org. Lett. 2006, 8, 479.

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23. Ethanol probably acts as a hydrogen source to facilitate the catalytic process, through β-hydrogen elimination of the intermediary π-allylpalladium ethoxide.

24. On the basis of the reported complexations of 1,1-difluoroallenes, the carbometallation takes place on the internal (fluorine-free) double bond. See: (a) Lentz, D.; Nickelt, N.; Willemsen, S.; Chem. – Eur. J. 2002, 8, 1205. (b) Lentz, D. J. Fluorine Chem. 2004, 125, 853. and ref. 14c.

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26. Use of pinacol (25 equiv.) instead of EtOH (50 equiv.) was not effective for the fluorinated system to afford 29a in 47% yield.

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