(S)-Methyl 3-(3,4-dimethoxyphenyl)-2-[2-(diphenylphosphanyl)benzamido]propanoate

Molecules of the title compound, C31H30NO5P, show a sttagered conformation about the C—C bond joining the dimethoxybenzene group to the chiral centre, with the dimethoxybenzene ring gauche to the amide group and anti to the ester group. In the crystal, weak intermolecular N—H⋯O and C—H⋯O hydrogen bonds form layers parallel to (110).

Molecules of the title compound, C 31 H 30 NO 5 P, show a sttagered conformation about the C-C bond joining the dimethoxybenzene group to the chiral centre, with the dimethoxybenzene ring gauche to the amide group and anti to the ester group. In the crystal, weak intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds form layers parallel to (110).

Comment
The title compound is being used as a precusor to novel chiral organocatalysts (Naicker et al. 2010 and2011). Analogous structures are well known precusors to several biologically active compounds (Zalán et al., 2006).
There is an analogous X-ray crystal structure reported (Clegg and Elsegood, 2003), which has a tert-butoxy group at the ester carboxyl carbon and a (9-H-Fluoren-9-yl)-methoxy group attached to the amide carboxyl carbon. The title compound has a methoxy and a 2-diphenylphoshinobenzene group at the these positions respectively.
The title compound exists in a well ordered staggered conformation about the C7-C8 bond (Fig. 1). As in the analogous X-ray structure, the dimethoxybenzene ring is gauche to the amide group and anti to the ester group. The configuration at C8 was confirmed to be S, on the basis of anomalous scaterring effects, Flack x parameter = -0.08 (6).
The molecules in the crystal are connected by relatively weak hydrogen bond interactions (Fig. 2) in which the N1-H1···O2 and the C10-H10A···O3 interactions give chains along the b axis. These chains are interconnected via the C21-H21···O4 interaction giving a layered packing system. Experimental 2-(diphenylphosphanyl)benzoic acid (1.3 g, 4.2 mmol) was dissolved was dissolved in DMF (15 ml) and THF (5 ml) followed by addition of HBTU (4.6 mmol), DIPEA (8.4 mmol) and (S)-methyl 2-amino-3-(3,4-dimethoxyphenyl)propanoate (1.0 g, 4.2 mmol). The reaction mixture was then stirred at room temperature until no more starting material could be detected by TLC analysis. The reaction mixture was poured into 30 volumes of chilled water; the mixture was then extracted thrice with ethyl acetate (20 ml). The combined extracts were dried over anhydrous sodium sulfate and then concentrated to dryness affording the crude product. This crude product was purified by column chromatography (50:50 EtOAc/Hexane, R f = 0.6) to afford the product 2.20 g (98%) as a white solid. M.p. = 420 K.
Recrystallization from ethyl acetate at room temperature afforded crystals suitable for X-ray analysis.

Refinement
All non-hydrogen atoms were refined anisotropically. All hydrogen atoms could be found in the difference electron density maps. H1N was thus positioned and refined freely with independent isotropic temperature factors. The other hydrogen atoms were placed with idealized positions and refined as riding on their parents atoms with U iso = 1.2 or 1.5 times U eq (C).