4-tert-Butyl-4′-(4-methoxyphenyl)-3′-(4-methylphenyl)-1,2,3,4-tetrahydrospiro[naphthalene-2,5′(4′H)-1,2-oxazol]-1-one

In the title compound, C30H31NO3, the tolyl ring is almost coplanar with the isoxazole ring [dihedral angle = 12.51 (7)°], whereas the methoxyphenyl ring is almost perpendicular to the isoxazole ring [dihedral angle = 89.77 (5)°]. In the crystal, molecules are connected through C—H⋯O hydrogen bonds, forming chains running along the a axis.


Comment
In the context of our research concerning the approach of dipole-dipolarophile in 1,3-dipolarcycloaddition, we have already studied the case where the dipole is an arylnitriloxide and the dipolarophiles are the 2-arylidenes of the 3,4-dihydronaphthalen-1-one substituted by anisopropyle group in position 4 (Al Houari et al., 2010).
We have shown that the ring closure reaction is highly regioselective and also highly diastereoselective. The relative configuration and conformation of the products have been determined by means of protonic magnetic resonance measurements.
In general, the majority or unique regiochemistry we observe in the 1,3-dipolarcycloaddition of arylnitriloxydes with ethylenic dipolarophiles leads to anisoxazoline, where the electron-attracting or withdrawing substitutent of the dipolarophile is in position 5 of the isoxazoline (Bruche & Zecchi 1983). This is exactly what we observed in our case with this X-ray crystal structure study, where the carbonyl group is in position 5 of the isoxazoline. We also found out, that the axial disposition the tert-butyl group imposes an exclusive anti approach of the dipole. This stereochemistry is due to steric effects.
The dihedral angles between the benzene ring of the naphthalenone and the two rings of the methylbenzene and the methoxybenzene are 58.79 (9)° and 85.36 (9)°, respctively. In the crystal, molecules are connected through C-H···O hydrogen bonds, forming chains running along the a axis.

Experimental
In a 100 ml flask, we dissolved 2 mmol of the 4-tert-butyl-2-(4-methoxybenzylidene)-3,4-dihydronaphthalen-1-one and 2.4 mmol of para tolyle oxime in 20 ml chloroform. The mixture was cooled to 0°C under magnetic stirring in an ice bath. Then 15 ml of bleach at 18°C was added in small doses without exceeding 5°C. The mixture was left under magnetic stirring for 16 h at room temperature, then washed with water until the pH was neutral and dried on sodium sulfate. The solvent was evaporated with a rotating evaporator and the oily residue was dissolved in ethanol. The precipitated product was then recrystallized in ethanol.