Ahatract-2Benxyloxypiperonal
15, a key intermediate in our synthesis of ( f ) -iso -/? -peltatin 7, was obtained by bromination of 4 -hydroxy -1,3 -benzodioxole 12, followed by treatment with (i) excess n-BuLi, (ii) N-methylformanilide, (iii) HCl/H,O, and (iv) benzyl chloride&CO,. The aromatic aldehydes 15 and 6 were subsequently transformed into the corresponding /? -(2 -alkoxy 3,4 -methylenedioxybenzyl) -y -butyrolactones 19 and 29, respectively. a-Hydroxyalkylation of 19 with 3,4,5-trimethoxybenldehyde 20, followed by cyclisation and hydrogenolysis afforded ( f ) -iso -fi -peltatin 7 in good yield. Similarly, a-hydroxyalkylation of 29 with UI and syringaldehyde 21, followed by cyclisation, afforded good yields of ( k) -iso -B -peltatin O-methyl ether 5 and ( k ) -iso -a -peltatin O-methyl ether 8, respectively.
Les structures des peltatines a et /I, respectivement 1 et 2, ont ttC propostes par Hartwell' et confirmees plus tard par Klemm.2 Ces deux composts ont etC isoles de Podophyllum peltatum (Podophylle).' L'Cther methylique 3 de la /?-peltatine a BtC isolt plus rkcemment de la plante mexicaine Bursera fag-arofdes4 Les peltatines 1 et 2 sont des lignanes connus comme ttant cytotoxiques et antitumoraux.s Ces composes se caracterisent par une jonction lactone trans (peltatine "A"),' le substituant phenyle Ctant pseudo-axial. OMe CHO c le substituant phenyle est pseudo-equatorial. Nous avons ainsi prepare l'ether methylique 5 de la ( + ) -is0 -B -peltatine, la ( &) -is0 -fl -peltatine 7 et l'ether mtthylique 8 de la ( &-) -iso -a -peltatine.