Thiele acetylation of quinones. Part III. p-Benzoquinones with bromo- and methoxy-substituents

Abstract

The three monobromo-monornethoxy-p-benzoquinones have been prepared ; they all undergo Thiele acetylation.The entering acetoxy-group is found orrho or para to the bromine atom in each of the triacetates. and never ortho to the methoxy-group.Thiele acetylation of the three isomeric dibromo-rnonomethoxy-p-benzoquinones and the three monobrornodirnethoxy-p-benzoquinones has been studied. Of these six compounds the only two which undergo the reaction are 2.6-dibrorno-3-rnethoxyand 2-bromo-5.6-dimethoxy-p-benzoquinone.

The bromoquinone annulation reaction: a formal total synthesis of EO9

“…Thus, 9 was synthesised in accordance with a literature procedure in three steps. 7 Close independent examination of the 1 H NMR of 7 and 9 showed that each was a pure regioisomer. However, when equimolar quantities of 9 and enamino ester 8 were dissolved in methanol at room temperature a remarkable transformation took place.…”

Convergent synthesis of 2H-chromenes—a formal [3+3] cycloaddition by a one-pot, three-step cascade

“…Except for the known 1b , 25 each of the bromoquinone starting materials was prepared according to the literature. 2-Bromo-5,6-dimethylbenzoquinone ( 1a ) 26 was prepared by oxidation of the known hydroquinone.…”

“…2-Bromo-5,6-dimethylbenzoquinone ( 1a ) 26 was prepared by oxidation of the known hydroquinone. 17 2-Bromo-5-methoxybenzoquinone ( 1c ) and 2-bromo-6-methoxybenzoquinone ( 1d ), were prepared according to Blatchly et al 25 and 2-bromojuglone methylether 1e was prepared according to Jung. 27 Quinone 1b was prepared by AgO oxidation of known compound 11 .…”

“…One-Pot procedure: From 2-bromo-3-methoxyquinone ( 3b 25 , 32.5 mg, 0.15 mmol) and vinyl stannane 2 (59 mg, 0.15 mmol) by the one-pot procedure by general procedure 6; reaction tim: 1 h (24.8 mg, 70%). Yellow oil: IR (neat) ν 3436, 2953, 1739, 1479, 1437, 1240, 1097, 1042, 800 cm -1 ; 1 H-NMR (acetone-d6) δ 7.78 (bs, 1H), 6.71 (dd, 1H, 3 J = 9.9 Hz, 4 J = 1.8 Hz), 6.78 and 6.49 (each d, each 1H, 3 J = 8.7 Hz), 5.91 (dd, 1H, 3 J = 9.9 Hz, 4.6 Hz), 5.36 (dd, 1H, 3 J = 4.6 Hz, 4 J = 1.8 Hz) 3.78 and 3.70 (each s, each 3H) ppm; 13 C-NMR (acetone-d6) δ 170.6, 147.0, 145.2, 144.4, 121.0, 120.9, 117.4, 115.8, 112.0, 73.5, 61.7, 52.5 ppm; LRFAB-MS: [M+Na] + = 259 (calc.…”

“…One-pot procedure: From the reaction of 2-bromo-5-methoxybenzoquinone ( 1c , 25 32.5 mg, 0.15 mmol) and vinylstannane 2 (59 mg, 0.15 mmol) according to general procedure 6; reaction time: 1.5 h. Yellow oil (22.5 mg, 64%).…”