Crystal structures of N-tert-butyl-3-(4-fluorophenyl)-5-oxo-4-[2-(trifluoromethoxy)phenyl]-2,5-dihydrofuran-2-carboxamide and 4-(2H-1,3-benzodioxol-5-yl)-N-cyclohexyl-5-oxo-3-[4-(trifluoromethyl)phenyl]-2,5-dihydrofuran-2-carboxamide

The structures of two butenolide derivatives are reported. The conformations are differ largely in the orientation of the amide carbonyl atom.


Chemical context
Butenolides, also known as furan-2(5H)-ones or furanones, are a recurrent moiety in more than 13,000 natural products (De Souza, 2005) and possess different assorted biological applications, exemplified by cytotoxic (Jung et al., 1990) and antibiotic (Sikorska et al., 2012) activities. Likewise, the butenolide derivative Vioxx1 is a potent NSAID (non-steroidal anti-inflammatory drug) used for the relief of pain and inflammation (Prasit et al., 1999) before it was withdrawn from the market in 2004. As a part of our scientific endeavors to access and mimic the complexity and diversity present in naturally occurring molecular scaffolds, the title compounds were synthesized using a Passerini/Knoevenagel sequence and the crystal structures are reported herein. Other multicomponent reaction-based approaches towards furanones have been reported, but they use limited starting materials. For example, they use unstable phosphonates (Beck et al., 2001), aliphatic substituents (Bossio et al., 1993(Bossio et al., , 1994Marcaccini et al., 2000), or tricarbonyl inputs (Rossbach et al., 2014).

Table 2
Hydrogen-bond geometry (Å , ) for (II). the position 5 carbon, TIFXIP (Beck et. al, 2001). For TIFXIP, the O1-C-C-O2 torsion angles for the two molecules in the asymmetric unit are À40.1 and 40.4 , similar to that found in (II), and the O1Á Á ÁO2 distances are 2.76 and 2.78 Å . When the search is expanded to include molecules with a second organic substituent on the furan 5-carbon, additional structures are found. In six structures, where only one of the substituents is an amide, the O1-C-C-O2 torsion angle is 180 AE 30 (À150 to 150 ); the value of À178.8 (1) found for (I) falls in this range.
For both compounds, crystals suitable for X-ray structure elucidation were obtained by slow evaporation of a solution of the compound in a mixture of ethyl acetate/hexanes (1:3).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms were visible in the difference Fourier maps for both structures. The hydrogen    atoms bonded to nitrogen atoms which are involved in hydrogen bonding were placed at positions of the electron density peaks and freely refined. All other hydrogen atoms were placed at calculated positions and allowed to ride on their parent atoms: C-H = 0.98 Å for methyl H atoms and 0.95 Å for other H atoms, with U iso (H) = 1.5U eq (C) for methyl H atoms and = 1.2U eq (C) for other atoms.
In (II), the trifluoromethyl substituent is disordered over two sets of sites with refined occupancies of 0.751 (3) and 0.249 (3). The disorder does not correspond to the expected rotational disorder of the -CF 3 group, but rather consists of a deviation, in the minor component, of the central carbon atom out of the plane of the aromatic ring.

(I) N-tert-Butyl-3-(4-fluorophenyl)-5-oxo-4-[2-(trifluoromethoxy)phenyl]-2,5-dihydrofuran-2-carboxamide
Special details Experimental. Absorption correction: SADABS-2008/1 (Bruker, 2009) was used for absorption correction. wR2(int) was 0.0543 before and 0.0350 after correction. The Ratio of minimum to maximum transmission is 0.7899. The λ/2 correction factor is 0.0015. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.