Nerol, allylic oxidation

It is noteworthy that allylic alcohols are oxidized to products with retained configuration of the olefinic bond. Geraniol and nerol were oxidized to the corresponding ( )-and (Z)-a-enals, respectively. As expected, primary alcohols were oxidized faster than secondary ones with the RuCl2(PPh3)3/BTSP system with relative rates from 20-40 1. The new system was applicable for the selective oxidation of primary-secondary diols... 

Such a simple mechanistic proposal accomodated the observation that highly activated, benzylic alcohols were good substrates due to the enhanced lability of their a-hydrogen atoms. In contrast, aliphatic alcohols are far less reactive towards H-radical abstraction and, accordingly, poor conversions should ensue. However, it was rather disturbing to note that allylic alcohols, such as geraniol and nerol, displayed poor reactivity in this system. Furthermore, it was observed that the aerobic oxidation of aliphatic alcohols invariably resulted in the rapid formation of a green copper(II) salt, with concomitant deactivation of the catalyst. 

Cinnamyl alcohol (1) and allylic alcohols of the terpenoid series, the "essential oils" of flowers, used as flavors and fragrances (geraniol, 2 nerol, 3 prenol, 4 carveol, 5 -ionol, 6) can be oxidized to the corresponding unsaturated carbonyl compounds in the presence of hydrated in 1,2-dichloroethane (1 atm 0, 70 °C) [23]. 

RuClg.(PPhg) catalyses the homogeneous oxidation by molecular oxygen of allylic alcohols (e.g., geraniol and nerol)... 

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