FIGURE 5.33 Shikimates from toluene.
under trade names such as Ambrofix, Ambrox, and Ambroxan. The conversion is shown in Figure 5.35. Initially, sclareol is oxidized to sclareolide (205). This was once effected using oxidants such as permanganate and dichromate but nowadays, the largest commercial process uses a biotechnol-ogical oxidation. Sclareolide is then reduced using lithium aluminum hydride, borane, or similar reagents and the resulting diol is cyclized to the naphthofuran. rf-Limonene (73) and valencene (206) are both extracted from citrus oils. Reaction of rf-limonene with nitrosyl choride gives an adduct that is rearranged to the oxime of /-carvone and subsequent hydrolysis produces the free ketone (105). Selective oxidation of valencene gives nootkatone (135).
Turpentine is obtained by tapping of pine trees and this product is known as gum turpentine. However, a much larger commercial source is the so-called crude sulfate turpentine (CST), which is obtained as a by-product of the Kraft paper process. The major components of turpentine are the two pinenes with a-pinene (65) predominating. Turpentine also serves as a source of p-cymene (83) and, as mentioned above, the shikimate anethole (53) (Zinkel and Russell, 1989).
Figure 5.36 shows some of the major products manufactured from a-pinene (65) (Sell, 2003, 2007). Acid-catalyzed hydration of a-pinene gives a-terpineol (74), which is the highest tonnage
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