Geranyl acetate allylic oxidation

The possible legioselecdvity and the preference for ( )>aUylic alcohol Hxxluction using the reoxida tive modification are demonstrated in a projected synthesis of cembranolides (equation 10). The substrate in this case contains two double bo and several allylic positions. This oxidation is reported to be even more selective than the aiudogous oxidation of geranyl acetate originally reported by Sh less. 

Oxidation reactions of this nature are common in the literature. For example, selenium dioxide in refluxing etiumolic solution brought about the allylic oxidative rearrangement geranyl acetate, which was further functionalized in a synthesis of the norsesquiterpenoid gytinidal (equation 46). This trans formation was also used in a total synthesis of phytol. Similarly, an a, -unsaturated aldehyde was obtained undm similar conditions in studies of a synthesis of pentalenic acid derivatives (equation 47). ... 

Allylic oxidation. The reaction was used by Meinwald and co-workers1 in the first step of a synthesis of gyrinidal (9),2 a norsesquiterpenoid from gyrinid beetles, from geranyl acetate (5). 

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. 

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