Ethyl 2-[N-(tert-butylsulfinyl)carbamoyl]benzoate

The title compound, C14H19NO4S, was obtained in quantitative yield by Lewis acid-catalysed alcoholysis of a phtalimide precursor. An intramolecular C—H⋯O hydrogen bond occurs. In the crystal, centrosymmetric dimers are formed by pairs of N—H⋯O hydrogen bonds between the sulfinyl O atoms and the carbamoyl N—H group of a neighboring molecule. C—H⋯O interactions feature in the crystal structure.

The title compound, C 14 H 19 NO 4 S, was obtained in quantitative yield by Lewis acid-catalysed alcoholysis of a phtalimide precursor. An intramolecular C-HÁ Á ÁO hydrogen bond occurs. In the crystal, centrosymmetric dimers are formed by pairs of N-HÁ Á ÁO hydrogen bonds between the sulfinyl O atoms and the carbamoyl N-H group of a neighboring molecule. C-HÁ Á ÁO interactions feature in the crystal structure.

Related literature
For a related compound, see: Harpp & Back (1973). For hydrogen-bond motifs and graph-set notation, see: Etter (1990); Bernstein et al. (1995). For potential applications of the title compound in the synthesis of enones, see: Wang et al. (2005). For standard bond lengths, see: Allen et al. (1987).  Table 1 Hydrogen-bond geometry (Å , ). Minakem is acknowledged for PhD funding (for AH). Dr J.-C. Daran is warmly acknowledged for his kind help during the preparation of this paper.

Comment
In the course of our studies on tert-butylsulfinyl phtalimide we have uncovered an unusual access to ethyl 2-(tertbutylsulfinylcarbamoyl)benzoate (I) based on the Lewis acid activation (for example by Samarium (III) salts) of one C=O bond of the phtalimide moiety. The title compound has been obtained quantitative yield.
Interestingly (I) exhibits one hydrogen donor (NH) and 5 electronegative atoms featuring available lone pairs that therefore should be able to act as hydrogen acceptors (4 oxygen and one sulfur). The combination of these donors and acceptors can induce a wide variety of hydrogen-bond patterns. A preferred one can be indicative of higher H-bond acceptor ability of one group.
Moreover, these features are of interest for potential applications in organocatalysis. Indeed acidic imide hydrogen atoms have been shown to favour organocatalytic processes in the formation of enones under mild reaction conditions. (Wang et al. 2005) The crystal structure clearly establishes N-H···O contacts between the O atoms of the sulfinyl groups and the NH groups since the N···O distance falls by more than 0.2Å below he sum of the van-der-Waals radii of the atoms involved. This is strongly indicative of the presence of two intermolecular hydrogen bonds. From that point, a cyclic dimer is observed with a R 2 2 (8) graph set (Fig. 2). Interestingly although isographic to the sulfinyl group (i.e. it has the same graph set but is chemically different), the carbonyl group of the amide is not involved in any hydrogen bond. This is a clear illustration of the higher polar character of the S=O bond making the sulfinyl oxygen a better H-bond acceptor than its carbonyl counterpart.
The R 2 2 (8) graph set is a six bonds ring system exhibiting a chair like conformation in which the two tert-butyl groups are in axial positions and the two carbamoyl units in equatorial positions (Fig. 2). An unexpectedly small distance (in the range of the sum of the van-der-Waals radii) is observed between the oxygen of the carboxyl group of the ester and the nitrogen.
The observed conformation might be minimizing the repulsive coulombic interaction and steric repulsions. All bond lengths and angles are otherwise normal. (Allen et al. 1987) Finally as the reaction has been carried out on racemic tert-butylsulfinyl phtalimide, (I) has been obtained as a racemate. It can be seen from the crystal structure that (I) crystallizes as a racemic compound (i.e. the two enantiomers forming dimers in the crystal lattice) indicating that no spontaneous resolution happens (formation of conglomerates).

Experimental
To a suspension of 100 mg (0.398 mmol) of tert-butylsulfinyl phtalimide in 5 ml of ethanol stirred at room temperature is added a solution of 24 mg (0.04 mmol) of samarium(III) trifluoromethanesulfonate in 5 ml of ethanol. After 0.5 h of stirring at room temperature a complete solubilization is observed and a full conversion is confirmed by TLC (cyclohexane/diethyl ether: 2/8). After concentration of the reaction mixture under reduced pressure, the remainings are diluted with 10 ml of dichloromethane and washed twice with water (2x5 ml). The aqueous phases are extracted twice with 10 ml of dichloro-methane. The combined organic phases are dried of sodium sulfate and concentrated to dryness under reduced pressure to give 118.1 mg (100% yield) of a white solid. Crystals of (I) suitable for X-ray diffraction were grown overnight at -20 °C in a 95/5 Diethyl ether/dichloromethane mixture.

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.98 Å (methyl) or 0.95 Å (aromatic) or 0.97 Å (methylene) with U iso (H) = 1.2U eq (C). The H attached to nitrogen has been located on difference Fourier and its coordinates were refined using N-H restraints of 0.88 (1) Å with U iso (H) = 1.2U eq (N). Fig. 1. ORTEP representation of (I) (Mercury; Macrae et al., 2008) with ellipsoids drawn at the 30% probability level.  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.