Simple Synthesis of l,3‐Dialkyl‐4,5‐dihalo‐2(3H)‐imidazolones

Abstract

slight effect on the bonding of the carbene carbon atom, but that the coordination octahedron of the metal is markedly distorted. The Ccarbene-Cr and Ccarbene--Cphenylene bond lengths are comparable with those found in other alkoxy(ary1)carbene complexes of chromium, only Ccarbene-O is slightly shorter (cf.l7]). The angles at Ccarbene are not unduly affected by the ring formation. The phenylene ring is essentially coplanar with the atoms of the two carbene groups and, within the standard deviations, shows no bond-length alternation.The coordination octahedron is distorted in two respects by the chelate effect of the biscarbene ligand (Ccarbene-Cr-Ccarbene angle of 81.3") (cf. [' I): 1. Since the trans--Ccarbene-Cr-CCO groups in the plane of the carbene ligands with 179.0 and 178.5" are almost linear and no bending of this plane takes place, the Cco-Cr-CcO angle of 82.3" is likewise very small, while the cis-Crarbene-Cr-Cco angles of 98.5 and 97.9" are distinctly widened.-2. The CO ligands perpendicular to the carbene plane are bent in towards the chelate ring and form an angle of 171.7(3)' with each other. ProcedureA suspension of Cr(C0)6 (2.5 g, 11.3 mmol) in 150 ml tetrahydrofuran is treated at 0°C with 80 ml of a 0 . 1 5~ solution of odilithiobenzene in ether and the mixture stirred for 1 h. The solvent is then removed and the residue is taken up in 100 ml of dichloromethane (-IOOC). A solution of triethyloxonium salt in CH2Cl2 is now added dropwise until the mixture no longer reacts alkaline, and, after 15 minutes' stirring, the mixture is evaporated to dryness. The crude product is chromatographed at -25°C with pentane/CH2CI2 (5 : 1) on silica gel. The eluate of the almost black zone is evaporated down, dissolved in pentane, and allowed to crystallize at -78°C; m.p. 115°C (I). (2) and (3) are obtained analogously; m.p. 104°C and 114"C, respectively.

Properties of haloimidazoles (review)

“…The 1-methyl derivatives 52a-d of 2,4,5-tribromo-(1) [41], 4(5)fluoro-(41) [42], 4,5-diiodo-2-methyl-(50) [43], and 3-chloro-5-diphenylimidazole (51) [44] were synthesized by their methylation with dimethyl sulfate (yields 54-91%). The alkylation of 2-haloimidazoles 53a-c with aralkyl bromides leads to the corresponding 1-aralkylsubstituted compounds 54a-c (yields 58-93%) [45][46][47].…”