Synthesis and paratropicity of heteroatom-bridged [17]annulenones

Abstract

Syntheses of 2,5 : 8,11 : 14,17-triepoxy[17]annulenone (2) by three methods are described. The first method involved Perkin-type condensation between 2,2′-bis-5-formylfuryl ketone (6) and furan-2,5-diacetic acid (7) and subsequent transformations. The second method involved Wittig reaction between (6) and furan-2,5-diyldimethylenebis(triphenylphosphonium chloride)(9). The third method, that preferred, used the Wittig reaction between carbonyldi(furan-2,5-diyl)dimethylenebis(triphenylphosphonium chloride)(15) and furan-2,5-dicarbaldehyde (16). Similarly the Wittig reaction of (1 5) and pyrrole-2,5-dicarbaldehyde (19) gave 8,11 -epimino-2,5 : 14,17-diepoxy[17]annulenone (1), and between (6) and thiophen-2,5-dimethylenebis(triphenylphosphonium chloride)(24) gave 2,5 : 14,17-diepoxy-8,11-epithio[17]annulenone (3). Lithium aluminium hydride–aluminium chloride reduction of annulenones (1)–(3) gave 7,10-epimino-1,4 : 13,16-diepoxycycloheptadeca-1,3,5,7,9,11,13,15-octaene (30), 1,4 : 7,10 : 13,16-triepoxycycloheptadeca-1,3,5,7,9,11,13,15-octaene (31), and 1,4 : 13,16-diepoxy-7,10-epithiocycloheptadeca-1,3,5,7,9,11,13,15-octaene (32). The paratropicity of (1)–(3) is discussed in terms of (30)–(32). as model systems. Reduction of (2) and (3) followed by methylation of the resultant alcohols gave 17-methoxy-1,4 : 7,10 : 13,16-triepoxycycloheptadeca-1,3,5,7,9,11,13,15-octaene (39) and the 7,10-epithioanalogue (40). The methyl ether (39) appeared to be paratropic.