Stereocontrolled synthesis of dehydrodendrolasin: Unstable polyene furanosesquiterpenoids

Marine furanosesquiterpenoids, (2E,4E,6E)- and (2Z,4E,6E)-dehydrodendrolasin (2) and (3), were synthesized in a geometrically controlled fashion. For the synthesis of 2, stereospecific addition of methyl(tributylstannyl)magnesium to E-enyne was employed effectively to afford (2E,4E)-3-(5-iodo-4-methyl-2,4-pentadienyl)furan (15). For the synthesis of 3, the key geometrical control for Z-enyne intermediate (7) was performed by a Pd catalyzed stereospecific hydrogenolysis of 3-(3-furyl)-1,1-dibromopropene (16) and successive Sonogashira coupling with trimethylsilylacetylene to give (2)-3-(5-trimethylsilyl-2-penten-4-ynyl)furan (18) in one pot. (C) 1997, Elsevier Science Ltd.