Friedel-Crafts Reactions of Some Conjugated Epoxides

Article abstract of DOI:10.1021/jo00152a036

The Friedel-Crafts (FC) reactions of (1,2-epoxyethyl)benzene, 1,2-epoxy-1-p-tolylethane, 1,2-epoxy-1-(p-methoxyphenyl)ethane, 1,2-epoxy-3-butene, and 1,2-epoxy-2-methyl-3-butene were examined under various conditions.Reaction time, temperature, Lewis acid, Lewis acid concentration, and solvent were varied.For (1,2-epoxyethyl)benzene (1), aromatic nucleophilicity was shown to be an important factor in promoting good FC yields.It was also shown that para carbocation stabilizing substituents on 1 did not improve FC yields.Vinyloxirane yielded primary products from direct ring opening (2-aryl-3-buten-1-ols) and conjugate addition (4-aryl-2-buten-1-ols) and secondary products (1,4-diaryl-2-butenes).Increased reaction time or catalyst concentration increases the proportion of secondary products.The primary and secondary FC pathways gave an excellent opportunity for study of the effects on product distributions of the use of aluminum chloride, boron trifluoride etherate, and stannic chloride Lewis acids.A significant FC reaction yield was not obtained with 1,2-epoxy-2-methyl-3-butene and toluene under the same conditions used for 1,2-eopoxy-3-butene.Presumably this results from steric effects.All products can be explained by attack of the aromatic nucleophile on the epoxide position (or positions) most capable of stabilizing incipient positive character.The epoxide is also less electrophilic than other alkylating agents under similar conditions.An explanation for this is given.