Crystal structure of (2R*,3R*)-3-amino-2-ethyl-N-(2-hydroxy-1,1- dimethylethyl)-3-p-methoxyphenylpropanamide, C17H28N2O3

Abstract

C17H28N2O3 ,t riclinic, P1 (no. 2), a =6 .098 A, b =1 1.703 A, c =1 2.721 A, 2 =8 1.95°, 0 =8 0.11°, / =7 7.35°, V =8 67.7 A 3 , Z =2 , Rgt(F) =0 .059, wRref(F 2 ) =0 .139, T =2 93 K. Source of material The title compound was synthesized according to [1] by treatment of 2-lithiated 2-alkyl-2-oxazoline with N-cumyl-2-p-metoxyphenylnitrone and subsequent reduction. To ap re-cooled ($78 °C) solution of alkyloxazoline (1.2 mmol) in 10 ml of THF under N2 was added s-BuLi (solution in cyclohexane, 1.4 M, 1.3 mmol). The resulting orange mixture was stirred for 15 min at this temperature before adding dropwise as olution of nitrone (THF, 5.0 ml, 1.0 mmol). Then, the reaction mixture was warmed up to room temperature, quenched with sat. aq. NH4Cl, poured into 20 ml of saturated brine, extracted with Et2 O( 30 ml), dried Na2SO4 and the solvent evaporated under reduced pressure. The crude mixture was filtered on silica gel (petroleum ether :A cOEt =8:2 ) to obtain am ixture [2] of equilibrating N-cumyl-3,3-dimethyl-8p-metoxyphenyl-9-methyl-9-ethyl-1,6-dioxa-4,7-diazaspiro[4,4]nonane and N-cumyl-2-methyl-1-p-metoxy-phenyl-2-(oxazolin-2-yl)hydroxylamine. To as olution of the mixture (0.5 mmol) in MeOH (5 ml) Pd on charcoal (10 %, w/w )w as added and the resulting mixture hydrogenated in Buchi Mini Clave apparatus at 10 bar overnight. Then the solution was filtered on celite pad and the solvent evaporated in vacuo affording the title compound as colorless crystals of inseparable mixture of diastereo-isomers with ratio 89/11 (after crystallization from hexane/Et2O, dr =9 5/5). The structure was confirmed by 1 H NMR, 13 CN MR, MS and IR, the data are available in the CIF. Experimental details Hydrogen atoms at nitrogen N1 were located by ad ifference Fourier and fixed during the refinement. Others Ha toms were geometrically positioned and included in the final refinement using the riding model approximation, with methyl d(C—H) =0 .96 A , methine d(C—H) =0 .98 A,m ethylene d(C—H) =0 .97 A,a romatic d(C—H) =0 .93 A, d(O—H) =0 .82 A, d(N—H) =0 .86 A and Uiso(H) =1 .5 Ueq for methylic groups, Uiso(H) =1 .2 Ueq for others groups. The large Rv alues are due to the poor quality of crystal. Solvent molecules were not found in the structure.