Oxidation by singlet oxygen of 4,7-dimethoxy-2,9-di-t-butyloxepino[2,3-b]benzofuran, an oxidation product of the antioxidant BHA

Abstract

Tetraphenylporphin-sensitized photo-oxidation of 4,7-dimethoxy-2,9-di-t-butyloxepino[2,3-6]benzofuran (3) and reaction of the products with methanol cleaves the oxepine ring, producing the acetal (9) and its isomer (13), which may be derived respectively from the 1,4-endoperoxide and 1,2-dioxetane oxygen adducts of (3). The geometrical isomerization of (9) to (14), and the acidcatalysed hydrolysis of (9), (1 3) and (14) to the dihydrofuranylidenebenzofuranone (1 8) are described.Crystal structures were determined for compounds (9), ( 14), and (18).

Reactions of ortho-quinones with ethoxycarbonylmethylene(triphenyl)-phosphorane. Trapping of the ortho-quinone methanide intermediates

“…Ethyl 2-oxo-2H-dibenzoV;h]chromene-4-carboxylate (1Oa) was obtained from quinone (5a) as yellow crystals (0.25 g, 7573, m.p. 158-159 "C (from EtOH) (lit.,, 158 "C); v,,,(KBr) 3 090, 2 940, and 1 725 cm-'; SH(80 MHz; CDCI,) 1.52 (3 H, t, J 7 Hz), 4.67 (2 H, d, J 7 Hz), 6.70 (1 H, s), 7.43-7.93 (5 H, m), and 8.25 8.67 (3 H, m); m/z 319 (2279,318 (M', 100), 290 (39,262 (17), 246 (ll), 245 (22), 218 (16), and 189 (41). The reaction between equimolar amounts of compounds (5a) and (6) under the same conditions also gave compound (10a) (45%).…”

“…(3), 274 (12), 272 (27), 270 (20), 249 ( 7 ) , 248 (lo), 247 (32), 246 (34), 245 (69), 244 (62), 243 (52), 242 (47), 220 (3), 218 (16) 15), 400 (M', 13), 369 (19), 367 (50), 365 (51), 362 (lo), 360 (14), 358 (41), 356 (71), 354 (58), 339 (22), 337 (23), 310 (18), 308 (19), 292 (38), 290 (38), 284 (54), 282 (loo), and 280 (79).…”

“…Conversion of Fumarate (W) into Diethyl 4,5,6tetrachlorophenyl) fumarate (16).-A mixture of compound (9d) (40 mg, 0.1 mmol), acetic anhydride (0.3 ml), and conc. sulphuric acid (2 drops) was stirred at room temperature for 6 h. The reaction mixture was poured into water (5 ml) and extracted with dichloromethane (3 x 3 ml).…”