Potassium Iodide → 2,2-dimethyl-6-iodo-7-nitro-2H-benzo[b]pyran

Participants

Reaction Conditions

Reaction Steps

To a cooled solution of 6-amino-2,2-dimethyl-7-nitro-2H-benzo[b]pyran (20.00 g, of the preparation of which was disclosed in British Pat. No. 1,548,222) in glacial acetic acid (800 ml) was added concentrated sulphuric acid (400 ml) and the solution stirred at 8° C. Nitrosyl sulphuric acid (prepared by dissolving sodium nitrite (6.62 g) in cold concentrated sulphuric acid (200 ml) the mixture being warmed to dissolve the solid then re-cooled to approximately 4° C.) was added keeping the temperature of the reaction mixture below 12° C. The dark, viscous mixture was stirred at approximately 7° C. for a further hour then poured into a cold (approx. 5° C.) solution of potassium iodide (15.27 g) in water (200 ml). Toluene (800 ml) was added to dissolve the resulting precipitate and the mixture stirred in an ice bath for 20 minutes, then at room temperature for 18 hours. The reaction mixture was diluted with water (500 ml), the organic phase was separated, washed with water, dried and evaporated in vacuo to afford the required 2,2-dimethyl-6-iodo-7-nitro-2H-benzo[b]pyran (11.84 g, 39%) as a red gum; nmr (CDCl3) δ 1.43 (s, 6H), 5.79 (d, J=10, 1H), 6.25 (d, J=10, 1H), 7.28 (s, 1H), 7.51 (s, 1H). This compound was used immediately in the next step. This crude benzopyran (11.74 g), cuprous cyanide (3.20 g) and anhydrous pyridine (450 ml) were heated under reflux for 8 hours. The mixture was concentrated to approximately half volume then diluted with water (1 liter) and the resulting emulsion extracted into ethyl acetate, the organic phase was washed with water, dried and evaporated in vacuo to afford a brown solid (9.62 g) which was purified on a silica gel column using ethyl acetate -60° -80° petroleum ether mixtures by a gradient elution technique, to give 6 -cyano-2,2-dimethyl-7-nitro-2H-benzo[b]pyran (4.00 g) as orange crystals. A small sample was recrystallised from ethyl acetate--60°-80° petroleum ether to yield orange crystals, mp 154°-155° C. nmr (CDCl3) δ 1.51 (s, 6H), 5.89 (d, J=10, 1H), 6.34 (d, J=10, 1H), 7.40 (s, 1H) 7.62 (s, 1H); ir (nujol mull) 2220, 1530, 1330 cm-1. Anal. Calcd. for C12H10N2O3 : C, 62.61; H, 4.38; N, 12.17. Found: C, 62.40; H, 4.51; N, 12.04%.

Provenance & Evidence