Epoxy-bridged [19]- and [21]-annulenones

Abstract

Wittig reaction between carbonyldi(furan-2,5-diyl)dimethylenebis(triphenylphosphonium chloride)(1) and 2,5-bis-(β-formylvinyl)furan (2) gave chiefly (6Z,8E,14E,16Z)-2,5:10,13:18,21-triepoxy[21]annulenone (4). Although the inner protons of annulenone (4) resonate at low field this is shown to be due to mutual steric compression rather than a paramagnetic ring current. A synthesis of 1,4-bis-(2-formylcyclohex-1-enyl)buta-1,3-diyne (20) is described. This on reaction with the salt (1) gave (6E,16E)-2,5:18,21-diepoxy-8,9:14,15-bis(tetramethylene)-10,11,12,13-tetradehydro[21]annulenone (24), which was also atropic. Wittig reaction between the salt (1) and 5-(β-formylvinyl)-2-furaldehyde (33) gave (6Z,12E,14Z)-2,5:8,11:16,19-triepoxy-[19]annulenone (34) which is diatropic.