(1S,3S)-Methyl 2-benzyl-6,7-dimethoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylate

In the title compound, C26H27NO4, the heterocyclic ring assumes a half-chair conformation and intermolecular C—H⋯O interactions help to construct the three-dimensional network within the crystal packing.

In the title compound, C 26 H 27 NO 4 , the heterocyclic ring assumes a half-chair conformation and intermolecular C-HÁ Á ÁO interactions help to construct the three-dimensional network within the crystal packing.

Experimental
The absolute stereochemistry of the crystal was confirmed to be S,S at C1 and C9 positions respectively by proton NMR spectroscopy. We recently reported the crystal structure of the R,S diastereomer at the C1 and C9 positions respectively. (Naicker et al., 2009) Interestingly, there are several significant differences between these diasteromeric crystals. The title compound crystallizes with monoclinic (P21) symmetry while its diastereomer has triclinic (P1)symmetry. Also the N-containing six membered ring assumes a half chair conformation [Q=0.5312 (16) Å, θ= 53.39 (17)° and φ=324.7 (2)°] as apposed to a half boat conformation (Fig. 1). This heterocyclic ring shape affects the position of the ester moiety relative to the phenyl ring at the C1 position. The torsion angle for C1-N1-C9-C10 is -171.7 (1)° while for the diastereomer this angle was 66.0 (2)°.
In addition, the N-benzyl and phenyl ring at C1 exisit in a cis orientation along the N1-C9 bond with a dihedral angle of 70.2 (2)° while for the diasteromer they are trans to each other with a dihedral angle of -64.7 (1)°. From the plain formed by the atoms C1-C2-C7-C8-N1-C9 the maximum displacement from planarity for N1 is 0.334 Å and for C9 0.360 Å.
A single intramolecular interaction between H11B and the phenyl ring attached to C12 (2.862 Å) is evident (Fig. 1). Two specific intermolecular short contacts originating from methoxy O1 and the ester O3 to different C-H groups (Fig. 2) link the molecules together in the crystal (Table 1). This arrangement results in chains parallel to the a axis. In the chain, the molecules are arranged so that their tails, linked by these C-H···O interactions, protrude to the outer edges of the chain, and their heads point towards the core of the chain.
Recrystallization from ethyl acetate at room temperature afforded colourless crystals suitable for X-ray analysis.