2-Oxo-4-trifluoromethyl-2H-chromen-7-yl 2-bromo-2-methylpropanoate

In the title compound, C14H10BrF3O4, the coumarin ring system is almost plannar (r.m.s. deviation = 0.025 Å) and a short C—H⋯F contact occurs. The propanoate fragment is orientated almost perpendicular to the ring [dihedral angle = 71.80 (12)°]. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, generating [100] chains.


Comment
The title compound C 14 H 10 BrF 3 O 4 , is a monofunctional coumarin derivative, which is used as an initiator (Sinkel et al. 2008) in Atom Transfer Radical Polymerization (ATRP). Being a monofunctional unit it can form end-functionalized linear polymers (Matyjaszewski et al. 2008;Stenzel-Rosenbaum et al.2001) when used as an initiator. Since most of the synthesized functionalized initiators are characterized by other techniques, their single crystal XRD reports are few.
The title compound is one such successful ATRP initiator which was crystallised from chloroform. It contains coumarin derivative with bromo methyl propanoate. The coumarin moiety is an important oxygen containing heterocyclic compound with diverse bioactivities such as non peptidic HIV protease inhibition and tyrosine kinase inhibition. Owing to such interesting properties, the synthesis of coumarin based initiators and their crystal structures are worth while to study.
One F atom (F1) lie in plane with the coumarin ring system and the other two F atoms are above and below the plane. The torsion angle of C6-C7-O3-C11 and C8-C7-O3-C11 are -114.21 (3)° and 71.42 (2)° respectively. The crystal is stabilized by intermolecular C-H···O hydrogen bond.
Experimental 7-Hydroxy-4-trifluoromethylcoumarin 5 g (0.02 mole), triethylamine 4.83 g (0.04 mole) and THF (400 ml) were placed in a 3-neck round bottomed flask. Bromoisobutyrl bromide 10.9 g (0.04 mole) was added slowly, using a syringe, with stirring, upon which an white precipitate of triethylammonium bromide was formed. The mixture was left to react for 6 hours, with stirring. Subsequently, triethylammonium bromide, the precipitate was removed by filtration and the THF was removed by rotary evaporation. The resulting crude product was dissolved in ethyl acetate, washed with bicarbonate solution and then with water thrice followed by brine solution and dried over anhydrous sodium sulphate. The resulting solvent was removed by rotary evaporation. The product was purified by column chromatography technique using 15% ethyl acetate in hexane as the eluent to obtain pure initiator as a bright white solid. Recrystallization of the compound from chloroform gave colourless blocks of (I).

Refinement
All hydrogen atoms were fixed geometrically and allowed to ride on the parent carbon atoms, with aromatic C-H = 0.93 Å and methyl C-H = 0.96 Å. The displacement parameters were set for phenyl H atoms at U iso (H) = 1.2U eq (C) and methyl H atoms at U iso (H) = 1.5U eq (C).  Fig. 1. View of (I) with atoms represented as 30% probability ellipsoids. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Br1 0.06908 (