6,7-Dimeth­oxy-3-meth­oxy­carbonyl-1-(2-meth­oxy­phen­yl)-3,4-dihydro­isoquinoline 2-oxide

Tricia Naicker; Thavendran Govender; Hendrik G Kruger; Glenn E M Maguire

doi:10.1107/S1600536811016539

. 2011 May 7;67(Pt 6):o1352. doi: 10.1107/S1600536811016539

6,7-Dimethoxy-3-methoxycarbonyl-1-(2-methoxyphenyl)-3,4-dihydroisoquinoline 2-oxide

Tricia Naicker ^a, Thavendran Govender ^a, Hendrik G Kruger ^b, Glenn E M Maguire ^b,^*

PMCID: PMC3120572 PMID: 21754746

Abstract

In the title compound, C₂₀H₂₁NO₆, an N-oxide-based organocatalyst, the N-containing six-membered ring adopts a twisted half-chair conformation. No hydrogen bonding or π–π stacking was found within the crystal structure.

Related literature

For related structures, see: Naicker et al. (2010 ▶, 2011 ▶).

Experimental

Crystal data

C₂₀H₂₁NO₆
M _r = 371.38
Monoclinic,
a = 5.4765 (1) Å
b = 21.9984 (6) Å
c = 15.0007 (4) Å
β = 92.774 (2)°
V = 1805.08 (8) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 173 K
0.25 × 0.18 × 0.15 mm

Data collection

Bruker APEXII diffractometer
7815 measured reflections
3959 independent reflections
3092 reflections with I > 2σ(I)
R _int = 0.016

Refinement

R[F ² > 2σ(F ²)] = 0.053
wR(F ²) = 0.157
S = 1.06
3959 reflections
245 parameters
H-atom parameters constrained
Δρ_max = 0.92 e Å⁻³
Δρ_min = −0.33 e Å⁻³

Data collection: APEX2 (Bruker, 2006 ▶); cell refinement: SAINT (Bruker, 2006 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: OLEX2 (Dolomanov et al., 2009 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811016539/hg5031sup1.cif

e-67-o1352-sup1.cif^{(20.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811016539/hg5031Isup2.hkl

e-67-o1352-Isup2.hkl^{(194.1KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811016539/hg5031Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors wish to thank Dr Hong Su of the Chemistry Department, University of Cape Town, for her assistance with the crystallographic data collection.

supplementary crystallographic information

Comment

The title compound is a novel N-oxide based catalyst containing a tetrahydroisoquinoline (TIQ) backbone. This is the first X-ray crystal structure report of this type of organocatalyst within this TIQ class of molecules. This compound and its derivatives are currently being tested in our laboratory as novel organocatalysts for asymmetric allylation reactions (Naicker et al. 2010).

From the crystal structure it is evident that the N-containing six membered ring assumes a twisted half chair conformation (Fig. 1). This differs from a similar structure that we recently reported which displays a twisted half boat conformation (Naicker et al. 2011). A possible reason for the change is the introduction of the oxygen atom O2 onto the sp2 hybridized nitrogen atom. All our previous examples have either a hydrogen or methyl group at that position.

Interestingly there is no classic hydrogen bonding within the crystal packing however, there are various intermolecular and intramolecular short contact interactions that link the molecules together within the crystal lattice. The N-oxide oxygen O2 displays two potential hydrogen bond interactions to C16—H16 and C20A—H20A which are 3.36 Å and 3.34 Å respectively. These interactions result in a layered packing within the crystal stucture as shown along the (100) axis in Fig. 2. A centroid distance of 7.156 Å indicated that there is no π-π stacking within the crystal matrix.

Experimental

(S)-methyl 6,7-dimethoxy-1-(2-methoxyphenyl)-3,4-dihydroisoquinoline-3-carboxylate (1.30 g, 3.7 mmol) was dissolved in dry methylene chloride (50 ml). Potassium carbonate (1.0 g, 7.5 mmol) was added and the reaction cooled to -78 °C. Meta-chloroperbenzoic acid (0.86 g of 75% pure, net 0.65 g, 3.7 mmol) was then added, and the reaction was allowed to stir at -78 °C for 3 h. At this time, the reaction was allowed to warm to room temperature. After stirring for a further 2 h at room temperature, methylene chloride (50 ml) was added to dilute the reaction and celite (500 mg) was added to aid filtration. The reaction was filtered, and the methylene chloride concentrated to dryness affording the crude product which was purified by column chromatography (methylene chloride:methanol, 99:1, R_f = 1/5) (1.20 g, 87% yield).

Melting point 423 K. [α]²⁰_D 5.128 (c 0.13 in CHCl₃).

IR (neat): 2923, 1742, 1508, 1285, 729 cm^-1.

¹H NMR (400 MHz, CDCl₃) δ 7.55 (dd, J = 7.5, 1.7 Hz, 1H), 7.51 – 7.42 (m, 1H), 7.20 – 6.97 (m, 3H), 6.74 (d, J = 6.5 Hz, 1H), 6.27 (d, J = 13.6 Hz, 1H), 4.94 (dt, J = 5.8, 2.9 Hz, 1H), 3.90 (d, J = 1.8 Hz, 4H), 3.77 (d, J = 4.3 Hz, 3H), 3.73 – 3.54 (m, 6H), 3.49 – 3.33 (m, 1H).

¹³C NMR (101 MHz, CDCl₃) δ 168.74, 157.23, 149.52, 148.17, 131.24, 131.12, 130.43, 122.89, 121.93, 121.49, 121.01, 120.80, 119.71, 112.05, 111.50, 110.64, 110.60, 110.08, 109.50, 77.34, 77.03, 76.71, 70.84, 70.72, 56.17, 56.11, 56.05, 55.93, 55.62, 53.24, 53.10, 30.80, 30.73.

Recrystallization from ethyl acetate at room temperature afforded colourless crystals suitable for X-ray analysis.