Cedrane oxide

Few synthetically useful examples of the oxidation of ethers by oxygen or ozone have been publish-ed.7 96 Q0 In 1978, Ourisson and coworkers reported that ozonization of the natural product cedrane oxide (43) on silica gel at -78 °C led to the formation of the corresponding lactone (44) in 30% yield (equation 32).A small amount of the tertiary alcohol (45) was also produced. Later, in the course of a chiral total synthesis of compactin, Hirama examined the ozonolysis of the alkene (46 equation 33). ° Under carefully controlled conditions, selective ozonolysis of the double bond could be achieved in 88% yield. However, when excess ozone was employed, significant amounts of the benzoate (47) were obtained, even at -78 C. In subsequent studies, benzyl ethers of primary and secondary alcohols,and carbohydrates were oxidized to the corresponding benzoates in excellent yields. Surprisingly, no further synthetic rqrplications of this reaction have been reported. 

Oxidation of cedranes and their derivatives by RuCyaq. Na(104)/CCl4-CH3CN (anhydrous RUCI3 does not work) was studied thus epicedrane was hydroxylated regioselectively with retention of configuration to 8a-cedranol (Fig. 4.4), and other oxyfunctionalisations of non-activated C-H bonds in cedranes were similarly accomplished (Table 4.1, cf. mech. Ch. 1) [69]. 

The CD spectra of six derivatives (60-65) of cedran-10-one devoid of a C(8)-C(i3) oxide bridge exhibit negative Cotton effects near 290 nm in accordance with the octant rule and a chair conformation of the six-membered ring151. The corresponding ketones with oxide bridge show a preference for a boat-like conformation and exhibit positive n —> jr Cotton effects152. 

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