The Zinc Chloride Catalyzed Migration of Halogen in the Claisen Rearrangement

Abstract

The zinc chloride catalyzed rearrangement of allyl 2,6-dichlorophenyl ether in riitrobenzene solution gave a good yield of 2-allyl-4,6-dichlorophenol along with some 2,6-dichlorophenol and 2-methj 1-5,7-dichlorocoumaran. The coumaran increased a t the expense of the 2-allyl-4,6-dichlorophenol. This is in contrast to the therillal rearrangement of this ether, which gave mainly 4-allj I-2,6-dichlorophenol along with smaller amounts of 3-allyl-6-chlorophenol and 2-allyl-4,6-dichlorophenol.

Halogen Migration and Elimination in the Claisen Rearrangement of Allyl 2,6-Dihalophenyl Ethers

“…In a recent publication (1) it was shown that the thermal Claisen rearrangement of allyl 2,6-dichlorophenyl ether gave not only the previously reported products, 4-allyl-2,6-dichlorophenol and 2-allyl-6-chlorophenol (2), but also a small yield (27,) of the halogen migration product, 2-allyl-4,6-dichlorophenol. The proportion of the halogen migration product increased to 7% and 11% respectively if the thermal rearrangement was conducted in nitrobenzene and in nitrobenzene containing lithium chloride.…”

Thermal Claisen rearrangement studies on 4,6- and 2,4-diacetylresorcinol bisallyl ethers: observation of loss or [1,5] sigmatropic shift of acetyl groups

“…band 2 (RF 0.36) gave 7-allyl-4-hydroxy-2-methyl-2,3-dihydrobenzofuran (4) (21).-A mixture of 4,6-diacetylresorcinol (1) (1.94 g, 10 mmol), N-bromosuccinimide (2.67 g, 15 mmol), and freshly distilled dioxane (25 ml) was refluxed for 10 h after which it was poured onto ice cold water (150 ml) with stirring. band 2 (RF 0.36) gave 7-allyl-4-hydroxy-2-methyl-2,3-dihydrobenzofuran (4) (21).-A mixture of 4,6-diacetylresorcinol (1) (1.94 g, 10 mmol), N-bromosuccinimide (2.67 g, 15 mmol), and freshly distilled dioxane (25 ml) was refluxed for 10 h after which it was poured onto ice cold water (150 ml) with stirring.…”

“….-A mixture of compound (21) (1 g, 3.6 mmol), allyl bromide (1 ml, 10 mmol), and freshly ignited potassium carbonate (5 g) was refluxed in dry acetone for 24 h. Work-up as for compound (2) afforded a pale brown precipitate which on crystallisation from aqueous alcohol gave the title compound (23) as colourless prisms (730 mg (23) in N,N-Dimethylani1ine.-Compound (23) (700 mg, 1.9 mmol) was refluxed in N,N-dimethylaniline (5 ml) for 6 h after which workup of the mixture gave a dark red gum (650 mg). It showed 10 spots on a t.1.c.…”

“…band 2 (RF 0.36) gave 7-allyl-4-hydroxy-2-methyl-2,3-dihydrobenzofuran (4) as a pale pink semisolid (30 mg, 8.7%) (Found: C, 75. (OH), 3 000, 1 615, 1 500, 1 440,990, and 910 cm-'; 6,(CDC13; Preparation of 5'-Acetyl-3'-bromo-2',4'-dihydroxyacetophenone (21).-A mixture of 4,6-diacetylresorcinol (1) (1.94 g, 10 mmol), N-bromosuccinimide (2.67 g, 15 mmol), and freshly distilled dioxane (25 ml) was refluxed for 10 h after which it was poured onto ice cold water (150 ml) with stirring. The resulting solution was treated with aqueous sodium hydroxide (20%) to decompose the excess of N-bromosuccinimide.…”

Synthesis of the Indole Nucleus

“…Furthermore, protonation of the oxygen moieties by the sulfurous acid would promote prototropic rearrangement, conceivably as shown in Eq. (228). The stability of aminochromes is markedly dependent upon the pH of the solution.6".…”