Synthesis and structure of photodegradable 1-(4,5-dimethoxy-2,3-dinitrophenyl)-2-methylpropyl N-butylcarbamate

1-(4,5-Dimethoxy-2,3-dinitrophenyl)-2-methylpropyl butylcarbamate, which affords butylamine on photoirradiation, was prepared by the reaction of 1-(4,5-dimethoxy-2,3-dinitrophenyl)-2-methylpropan-1-ol and butylisocyanate using dibutyltin dilaurate as a catalyst. Single crystals of the carbamate were grown in a 1:1 mixed solution of hexane and ethyl acetate. Two nitro groups and one methoxy group of the novel photo-protecting group were twisted out of the plane of the aromatic ring and intermolecular hydrogen bonds are observed between carbamate moieties.


Chemical context
Photodegradable protective groups (PPGs) are common tools in the field of organic, biochemical, and materials sciences (Cambie et al., 2016;Ellis-Davies, 2020;Hansen et al., 2015). 2-Nitrobenzyl groups are widely used as PPGs because several precursors are available, they react with various functional groups and the resulting protected compounds are soluble in common organic solvents. To increase the sensitivity of 2-nitrobenzyl-group-protected derivatives, several chemical modifications, such as the introduction of substituents at theposition, have been performed (Kasuga et al., 2016;Zhao et al., 2012).
Herein, we report the synthesis and structure of the novel photolabile title compound 1-(4,5-dimethoxy-2,3-dinitrophenyl)-2-methylpropyl N-butylcarbamate (1), which has an isopropyl group at the -position and an additional nitro group at the 3-position. It was prepared from the corresponding alcohol and isocyanate using a tin catalyst based on a previously reported reaction with modifications (Stegmaier et al., 2008) and the amine was released upon photoirradiation, which indicated that the compound has high reactivity and the potential for application in various functional materials. Compound 1 exhibits a higher sensitivity to light than the corresponding compound with one nitro group at the ortho position (Kasuga et al., 2015).

Structural commentary
The asymmetric unit of 1 contains a single molecule in which four functional groups and a carbamate linkage site are connected to the aromatic ring. The substituents are positioned in a manner that prevents steric repulsion (Fig. 1).
In the related compound, 4,5-dimethoxy-2-nitrobenzyl acetate (shown in the scheme below), the nitro and dimethoxy groups are in the same plane as the aromatic ring and the whole molecule is flat in the absence of substituents at theposition (Kasuga et al., 2015).

Supramolecular features
In the crystal, N3-H3Á Á ÁO8 i hydrogen bonds link the molecules into chains parallel to the a axis ( Fig. 2 and Table 1).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The C-bound H atoms were positioned geometrically (C-H = 0.93-0.98 Å ) and refined using a riding model with U iso (H) = 1.2 or 1.5U eq (C).   (Rigaku OD, 2018); program(s) used to solve structure: ShelXT (Sheldrick, 2015aa); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: Olex2 (Dolomanov et al., 2009); software used to prepare material for publication: Olex2 (Dolomanov et al., 2009). 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.