Preparation of 3-(10′-halo-9′-anthracenyl) isoxazolecarboxylic esters

The 10-halo (Cl or Br) anthracene-9-nitrile oxides (1a,b) were obtained directly from the treatment of 9-anthracenylaldoxime with N-halosuccinimide (NCS or NBS) in DME The 3-(10'-halo-9'-anthracenyl)-5-isoxazolecarboxylic esters (5a,b and 6a,b) were prepared via 1,3-dipolar cycloaddition between the obtained nitrile oxides 1a (or 1b) and two different dipolarophiles: ethyl beta-pyrrolidinocrotonate (an enamine of ethyl acetoacetate) or dimethyl acetylenedicarboxylate (DMAD) respectively. The 10 (or 10')-position of the anthracene in either anthracene-9-nitrile oxide or 3-(9'-anthracenyl) isoxazole molecules (3,4) is readily halogenated by N-halosuccinimide in DME X-ray studies showed that 5a possesses two aromatic ring systems that lie at 74.4degrees from coplanarity. The bond linking the two ring systems is 1.4893(18) Angstrom, indicating only partial conjugation between the two ring systems. The crystal lattice showed unique head-to-tail intermolecular stacking of anthracene rings.