Bromomethyl ß-styryl and ß-bromostyryl sulfones in the Michael-induced Ramberg-Bäcklund reaction

The UV-initiated addition of bromomethane sulfonyl bromide to phenylacetylene (quartz test tube, CH2Cl2, 20 °C) gives bromomethyl (E)-2-bromo-2-phenylethenyl sulfone. In a similar reaction with styrene, bromomethyl 2-bromo-2-phenylethyl sulfone is formed. Subsequent dehydrobromination of this adduct (Na2CO3 in aqueous dioxane, 20 °C) gives bromomethyl (E)-2-phenylethenyl sulfone, which is transformed by bromination-dehydrobromination (Br2 in CCl4 at 20 °C, then Na2CO3 in aqueous dioxane, 50 °C) into bromomethyl (Z)-1-bromo-2-phenylethenyl sulfone. Upon heating in methanol in the presence of sodium methoxide, the unsaturated sulfones enter the Michael-induced Ramberg-Bäcklund reaction. Monobromo-substituted derivative transforms into 1-(1-methoxy-2-propenyl)benzene. Dibromosubstituted derivatives give 1-(1,1-dimethoxy-2-propenyl)benzene via intermediate formation of bromomethyl 2-methoxy-2-phenylethenyl sulfone through elimination-addition or vinylic substitution.