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between Lawesson’s reagent and allyl arylamides derived from
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irradiation in sulfolane at 180 °C was enough to raise the
yield of 4 to 89% (Table 2, Type A). The yields of 4 were
significantly improved compared to the experiments with-
out microwave (Table 1). The reason may be that the C–Cl
bond and K–F bond were weakened by microwave irradi-
ation, which promoted the formation of Meisenheimer
intermediate (Behbehani and Ibrahim 2015). Besides, the
use of high boiling point solvents, such as xylene and
sulfolane, improved the yields to 63 and 91%, respectively.
The pressurized microwave reactor (Type B) for the
fluorination offered a broader temperature range and
facilitated heating above the normal boiling point of the
solvent, as well as possible benefits of the pressure effect.
For instance, the yield further increased and the reaction
time was reduced to 5 h in the reaction at 180 °C in xylene,
probably because the solvothermal conditions in the closed
reactor contributed to the fluorination. However, this
method was useless in the reaction at 280 °C in sulfolane,
probably due to the severe decomposition of sulfolane and
catalyst at high temperature. Although the yield of 4 was
moderate in the case of xylene, this route is limited by the
application range and discontinuity.
Boswell GA Jr, Ripka WC, Scribner RM, Tullock CW (1974)
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co-loaded ultrathin TiO2 nanosheets for photocatalyzed H2
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dilution method for preparation of 1,1,2,2,9,9,10,10-octaflu-
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Conclusions
We developed a practical and fast microwave-assisted
protocol for preparation of 4 from commercially available
5 and cheap KF in a composite PTC system (3 mol%
Ph4PCl and 1 mol% 18-crown-6) in sulfolane at 180 °C.
The introduction of microwave increased the yield and
significantly shortened the reaction time from dozens of
hours to a few hours. Further explorations of the reaction
mechanism are under progress and will be reported.
Gorham WF (1966) A new, general synthetic method for the
preparation of linear poly-p-xylylenes. J Polym Sci Part A
Hicks C, Duffy B, Hargaden GC (2014) Synthesis and modification of
octafluoro[2.2]-paracyclophane (parylene AF4). Org Chem Front
Acknowledgements This work was financially supported by the
National Natural Science Foundation of China (Nos. 21276050 and
21406034), Fundamental Research Funds for the central Universities
(No. 3207045414).
Jha M, Davis C, Fazzari J, Vitali M (2014) BF3 etherate-mediated
microwave-assisted facile synthesis of thiopyrano[2,3-b]indol-2-
¨
Koivula T, Simecek J, Jalomaki J, Helariutta K, Airaksinen AJ (2011)
A comparative study on the effect of solvent on nucleophilic
fluorination with [18F] fluoride: protic solvents as co-solvents in
SN2 and SNAr reactions. Radiochim Acta 99:293–300. doi:10.
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