trans-4-Nitrophenyl 4-(tosyloxymethyl)cyclohexanecarboxylate

The title compound, C21H23NO7S, is an important intermediate in the synthesis of poly(amidoamine) dendrimers. The cyclohexane ring adopts a chair conformation. The dihedral angle between the two aromatic rings is 69.5 (2)°. The molecules are linked into a zigzag chain along the b axis by C—H⋯O hydrogen bonds.

The title compound, C 21 H 23 NO 7 S, is an important intermediate in the synthesis of poly(amidoamine) dendrimers. The cyclohexane ring adopts a chair conformation. The dihedral angle between the two aromatic rings is 69.5 (2) . The molecules are linked into a zigzag chain along the b axis by C-HÁ Á ÁO hydrogen bonds.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: CI2549).

Comment
Activated esters are commonly used in peptide synthesis to facilitate the reaction of carboxylic acid and amine to obtain amide. trans-Nitrophenyl ester of N-protected amino acid can react with amino group quickly at room temperature with fairly good yields (Sewald et al.,2002). In our work, cyclohexane derivatives were designed to be linked to poly(amidoamine)dendrimer[PAMAM] through the amide bond which could be formed by the reaction of terminal amino groups of PAMAM dendrimer and cyclohexanecarboxylic acid. So the title compound, a p-nitrophenyl ester of trans-4-(tosyloxymethyl) cyclohexanecarboxylic acid was synthesized. As expected, the modification of periphery of PAMAM dendrimer effectively is realised under mild conditions. We report here the crystal structure of the title compound.
The molecules are linked into a zigzag chain along the b axis by C-H···O hydrogen bonds (Table 1).
Experimental trans-4-(Tosyloxymethyl)cyclohexanecarboxylic acid (10 mmol) and p-nitrophenol (11 mmol) were dissolved in ethyl acetate (10 ml) and the solution was cooled to 273 K in an ice bath. Then a solution of DCC (11 mmol) in ethyl acetate (5 ml) was added dropwsie with stirring. After the addition, the stirring was continued for 30 min at 273 K and for 24 h at room temperature. Then acetic acid (0.5 ml) was added and after 30 min the reaction solution was filtered and the filtrate was evaporated to leave a yellow solid. The title compound was recrystallized from acetone. Single crystals suitable for X-ray analysis were obtained by slow evaporation of a acetone-water solution at room temperature.

Refinement
H atoms were positioned geometrically (C-H = 0.93-0.98 Å) and refined using a riding model, with U iso (H) = 1.2-1.5U eq (C). Fig. 1. The molecular structure of (I), showing the atomic numbering scheme. Displacement 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 > 2sigma(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.