The Interaction of Polyfluorinated β-diimines And Perfluorocarboxylic Acids' Fluoroanhydrides

D. U. Verbitsky, * M. A. Kurikin

 A.N.Nesmeyanov Institute of Organoelements Compounds RAS. 119991, Vavilova str.28, Moscow, Russia,
 Fax (499) 135 5085. E-mail: mak@ineos.ac.ru

The tris-(perfluoroalkyl)pyrimidines synthesis methods based on the reaction of polyfluorinated β-diimines and perfluorocarboxylic acids fluoroanhydrides has been developed

The condensation of polyfluorinated β-diimines (1) with acylhalogenides resulting in forming of 2,4,6-trisubstituted pyrimidines [1] opens wide opportunities for synthesis of new biologically active compounds and monomers as well.

Before [2] it was proved, that at interaction with perfluorocarboxylic acids' anhydrides and chloroanhydrides the diimines (1) form 2,4,6-tris-(perfluoroalkyl)-5-fluoropyrimidines (2).

The distribution of this reaction over industrially available perfluorocarboxylic acids fluoroanhydrides (3) is of obvious interest from the practical point of view.

The present work is dedicated to the topic. The β-diimines (1) appeared to interact with fluoroanhydrides (3) at room temperature in the solution of absolute diethyl ether. However the yields of isolated required pyrimidines (2) appeared to be very low (~40%). Along with that the products of acidic decomposition of initial diimine (for R_F = CF₃ - tetrafluoroaceton and trifluoroacetic acid) were detected in the reaction mass.

The condensation discussed in this review is followed by the isolation of by-products - water and acid, which interaction with the initial diimine (1) results in its destruction. This process is likely to be put into practice in case of using any of acylating reagent (anhydride, chloro- or fluoroanhydride). If condensation is being realized in a quick way (anhydride, chloroanhydride), then the decomposition of -diimine (1) will occur at an insignificant grade.

In case of fluoroanhydrides (3) differing from corresponding chloroanhydrides by their lowered reactivity in analogous processes [3], the acidic decomposition of β-diimines (1) starts to compete with the main reaction. Indeed, when carrying out the condensation of diimines (1) and fluoroanhydrides (3) over acid acceptor (pyridine) the side process associated with the hydrolysis of compounds (1) was managed to put down and pyrimidines (2) were isolated with preparatory yields (up to 87%).

Experimental

NMR ¹⁹F spectra were registered at "Bruker AC-200F" spectrometer (188,3 MHz). Chemical shifts are given in ppm with CF₃COOH as  standard, the coupling constants reported in Hz.

Perfluoro-2-hexyl-4-butyl-6-methylpyrimidine (2c, R'_F = n-C₆F₁₃)

1. In the absence of pyrimidine.
 The solution of 7.0g (18.7 mmole) of diimine (1c) in 100 ml of absolute ether was put into two-neck flask equipped with the backflow condenser and drop funnel. Afterwards during mixing (magnetic stirrer) 16.4 g (44.8 mmole) n-C₆F₁₃COF were added dropwise (~ 2 hours). The reaction mass was neutralized by aqueous solution of NaHCO₃, the organic layer was separated, flashed  out with water (2X150 ml), dried over CaCl₂. 5.5 g (42%) (2c), boiling point 110-113^oC (22 mm Hg) were obtained by distillation.

2. Over pyrimidine.
The solution of 15.5 g (41.4 mmole) of diimine (1c) and 12.8 g (162.0 mmole) of dried pyrimidine in 100 ml of absolute ether was put into two-heck flask equipped with the backflow condenser and drop funnel. Afterwards during stirring (magnetic stirrer) 34.7 g (94.8 mmole) n-C₆F₁₃COF (~ 2 hours) were added dropwise. The reaction mass was poured into water, the organic layer was separated, washed with the water (2X150 ml) and dried over CaCl₂. 19.5g (67%) (2c) were obtained by distillation.

Analogously other perfluoropyrimidines were synthesized (2); the details of experiments as well as the spectrum information and physical constants of obtained compounds are listed in Table 1.

References

1. O.E. Petrova. Diss. kand. khim. nauk, INEOS RAS, Moskva, 2003, 122s.

2. O. E. Petrova, M.A. Kurykin, D.V. Gorlov, Izv. AN, Ser. Khim.‚ 1999, N 11, 2195.

3. N.O. Calloway, J. Am. Chem. Soc., 1937, 59, 1474.

Table 1.