AROMATIC COPE REARRANGEMENT - THERMAL-REACTIONS OF CIS-1-ARYL-2-VINYLCYCLOPROPANES

At 140-150 ΔC cis-1-phenyl-2-vinylcyclopropane (1c) undergoes ds ⇋ trans interconversion with ΔH‡=32 kcal/ mol, ΔS‡=-5.8 eu, at or above 200 ΔC formation of 4-phenylcyclopentene occurs. Attempts to trap the Cope rearrangement product, bicyclo[5.4.0]undeca-l, 4, 8, 10-tetraene (3), via Diels-Alder adducts failed. Heating 1c with potassium trans-bu-toxide at 150 ΔC gave 1-phenyl-1, 3-pentadiene (4). This product was formed only from 1c, in the presence of trans-butyl alcohol-O-d recovered 1c and 1t were devoid of deuterium. A route to 4 via formation of a tetraenide ion from 3 followed by ring opening is postulated. Treatment of cis-1-(m-methoxyphenyl)-2-vinylcyclopropane (7c) with ethyl mercaptide gave cis-l-(m-hydroxyphenyl)-2-vinylcyclopropane (8c). Heating 8c at 120 ΔC gave 6, 9-dihydro-5H-benzocyclohepten-1-ol (10). Treatment of cis-l-(p-methoxyphenyl)-2-vinylcyclopropane gave only (trans-1-(p-hydroxyphenyl)-2-vinylcyclopropane. The relevance of these results to the aromatic Cope rearrangement is discussed. © 1978, American Chemical Society. All rights reserved.