Geranyl acetate reduction

Surprisingly, linalyl acetate (R = OAc) fails to undergo reduction under these conditions instead, it rapidly decomposes through cyclization and polymerization pathways.205 The same reaction conditions transform geranyl p-tolyl sulfone (R = S02C6H4Me-/ ) into a mixture of 7% reduced and 93% cyclized products within 20 hours, whereas geranyl acetate (R = OAc) gives only a 20% yield of cyclized and no reduced product (Eq. 95) 205... 

We mentioned earlier the epoxidation of geranyl acetate using the UHP method. Conventional epoxidation of geraniol using MCPBA results in the formation of a 2 1 mixture of the 6,7-epoxide and the 2,3-isomer despite the reduction in electron density at the 2,3-position caused by the allylic hydroxyl group [29]. In this connection it is interesting to note that the 2,3-epoxide is formed in a 93% yield by using an emulsion technique in which the 6,7-double bond is kept away from the MCPBA in a hydrocarbon phase [30]. 

For the synthesis of aleuriaxanthin (81), geranyl acetate (1) was chosen as starting material. Oxidation of a terminal methyl group with Se02, followed by reduction, gave the allylic alcohol 2 which was subjected to a Sharpless epoxidation to give the epoxide J in a yield of 68% [1] (Scheme 3). 

In the 1980s, the Japanese firm Kuraray developed a stereoselective Vitamin A synthesis, which follows the Cm + Cm concept. The synthetic building blocks are cyclogeranyl phenyl sulfone and a Cm-aldehyde, which is obtainable by allylic oxidation of geranyl acetate with t-butyl hydroperoxide. [81] The alcohol function is protected as the THP-ether, and the sulfmic acid and hydroxytetrahydro-pyran are eliminated with potassium fbutoxide in petroleum ether. By means of this double elimination, the reduction step is avoided. 

Steroids are members of a large class of lipid compounds called terpenes. Using acetate as a starting material, a variety of organisms produce terpenes by essentially the same biosynthetic scheme (Fig. 8). The self-condensation of two molecules of acetyl coenzyme A (CoA) forms acetoacetyl CoA. Condensation of acetoacetyl CoA with a third molecule of acetyl CoA, then followed by an NADPH-mediated reduction of the thioester moiety produces mevalonic acid [150-97-0] (72). Phosphorylation of (72) followed by concomitant decarboxylation and dehydration processes produce isopentenyl pyrophosphate. Isopentenyl pyrophosphate isomerase establishes an equilibrium between isopentenyl pyrophosphate and 3,3-dimethylallyl pyrophosphate (73). The head-to-tail addition of these isoprene units forms geranyl pyrophosphate. The addition of another isopentenyl pyrophosphate unit results in the sesquiterpene (C15) famesyl pyrophosphate (74). Both of these head-to-tail additions are catalyzed by prenyl transferase. Squalene synthetase catalyzes the head-to-head addition of two achiral molecules of famesyl pyrophosphate, through a chiral cyclopropane intermediate, to form the achiral triterpene, squalene (75). 

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