Rubottom procedure

In addition to uvidins A (3.14) and B (3.36) (10), more recently several new fatty acid esters of drimenol (3.2-3.6) and uvidin A (3.16-3.20) (11), and three new sesquiterpenes (12) with the bicyclofarnesane skeleton have been isolated from L. uvidus (Table 3). The stereostructures of the three uvidins C (3.29), D (3.34), and E (3.22) have been established by speetroscopic data and chemical reactions (12). In the interesting synthesis of uvidin E (3.22) from uvidin A (3.14), the Rubottom s procedure was employed for the regiospecific and stereoselective a-hydroxylation at C-5 of the enone 3.10 (12) (Scheme 2). 

Rubottom, G. M., Vazquez, M. A., Pelegrina, D. R. Peracid oxidation of trimethylsilyl enol ethers. Facile a-hydroxylation procedure. Tetrahedron Lett. 1974, 4319-4322. 

Regioselective addition of hydroxylamine to 2-acetyl-3-hydroxy-2-cyclohexen-l-one to yield one of two possible dihydrobenzisoxazolones, specifically 3-methyl-6,7-dihydro-l,2-benzisoxazol-4(5)-one, has been reported by Smith (2) and by Akhiem et al (IQ). By means of this procedure, 7 (R = n-C i H23) was converted to the corresponding isoxazole derivadve 8 8, in contrasrm 7, possesses only one enolizable position, and while hydrogens at position 7 are presumably somewhat acidic, we anticipated them to be less acidic than those a to the carbonyl, the intended site of attack. A Rubottom hydroxylation (H) of 8 did, in fact, provide the analog 9 with the OH at the necessary position. 

An olefinic bond in the acyl side chain presents a site for undesired reaction during two steps in the above procedure. First is the potential for epoxidation during the introduction of the oxygen by m-chloroperbenzoic acid of the Rubottom hydroxylation. Second is e likelihood of hydrogenation during the catalytic r uction of the N-O bond of 9. 

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