Crystal structure of 2-oxo-2-phenylethyl diisopropylcarbamate

In the molecular structure of the title compound, the urethane function and the benzoyl group are almost perpendicular to each other [dihedral angle 88.97 (5)°]. In the crystal structure, infinite supramolecular layers in the bc plane are formed by weak C—H⋯O hydrogen bonds.


Chemical context
Phenacyl and desyl compounds have been a subject of interest for many years due to their use as photoremovable protecting groups (PPGs) (Givens et al., 2012;Kammari et al., 2007;Klá n et al., 2013;Sheehan & Umezawa, 1973). Carbamates are used for the protection of carboxylic acids and may also act as suitable protecting groups for amines (Speckmeier et al., 2018). Speckmeier and co-workers synthesized several phenacyl urethanes, but the protection of diisopropylamine by a phenacyl group has not been reported so far. The title compound was synthesized according to reported routes (Speckmeier et al., 2018).

Structural commentary
As expected, the carbamate functional moiety (N1/C3/O3/O2) is essentially planar (maximum deviation of 0.01 Å for C3). The same is true for the benzoyl group (C1/O1/C10-C15, maximum deviation of 0.05 Å for O1). These two planes subtend a dihedral angle of 88.97 (5) and therefore an almost perpendicular arrangement (Fig. 1). Otherwise, the bond lengths and angles are of expected values with C3-N1 [1.348 (2) Å ] and C3-O2 [1.368 (2) Å ] being slightly shorter than a typical C-O or C-N single bond due to the partial double-bond character of the respective bonds in a carbamate.

Supramolecular features
The crystal structure of the title compound features weak hydrogen bonds (Desiraju & Steiner, 2001) of the C-HÁ Á ÁO type, as shown in Table 1. The interaction C5-H5BÁ Á ÁO3 ISSN 2056-9890 links molecules of the title compound into infinite chains parallel to the c-axis direction. Additional C2-H2BÁ Á ÁO1 and C9-H9BÁ Á ÁO2 interactions link these infinite chains to a supramolecular sheet parallel to the bc plane (Fig. 2). The latter interaction is accompanied by a short C9-H9BÁ Á ÁC3 contact, which makes the contact look like a non-classical hydrogen bond towards the -system of a C O double bond, again showing the partial double-bond character of the respective bond.

Database survey
In the CSD (ConQuest Version 2020.3.0; Groom et al., 2016), only one other carbamate with a CH 2 -C(O)-Ph group attached to the carbamate oxygen atom is reported (NIWQUI; Jiang et al., 2019). The respective compound shows a diethylamino group and a p-chlorophenyl substituent instead of the diisopropylamino group and the non-substituted phenyl group in the title compound. In contrast to the title compound, the carbamate plane and the benzoyl plane are almost coplanar. The carbonyl oxygen atoms show numerous short contacts towards different C-H groups of neighboring molecules, leading to a dense three-dimensional network.

Synthesis and crystallization
Diisopropylamine (0.05 mol, 5.05 g) and 1 equiv. of cesium carbonate (0.05 mol, 16.55 g) were placed in a Schlenk tube and dissolved in anhydrous DMSO (150 mL). The tube was sealed with a septum and two balloons filled with CO 2 were bubbled through the reaction mixture within one h while stirring. After the addition of CO 2 , 1.1 equiv. of 2-bromo-1phenylethan-1-one (0.055 mol, 10.95 g) dissolved in a small amount of DMSO was added in one portion. The consumption of 2-bromo-1-phenylethan-1-one was monitored by TLC and after 30 min the reaction mixture was poured on ice to quench the reaction. After extraction with dichloromethane (3Â), the combined organic phases were washed with brine, separated and dried over Na 2 SO 4 . The solvent was removed in vacuo and the crude product was recrystallized from n-hexane/ethanol (4:1) to afford the title compound (12.90 g; 98%) as a colorless solid, m.p. 347.5 C. 1 Table 1 Hydrogen-bond geometry (Å , ).  (2)  157 Symmetry codes: (i) x; y À 1; z; (ii) x; Ày þ 3 2 ; z þ 1 2 ; (iii) x; y þ 1; z.

Figure 2
Crystal structure of the title compound showing layers of molecules along the bc plane that are built up by C-HÁ Á ÁO hydrogen bonds.

2-oxo-2-phenylethyl diisopropylcarbamate
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.