Studies on the syntheses of sesquiterpene lactones. 11. The syntheses of 3-epizaluzanin C, zaluzanin C, zaluzanin D, and related compounds 3.alpha.-hydroxyguaia-1(10),4(15),11(13)-trieno-12,6.alpha.-lactone and 3.alpha.-hydroxyguaia-4(15),9,11(13)-trieno-12,6.alpha.-lactone