Monoperphtalic acid

In the other synthesis of the diol (41) from the sclareol (3) [63], the latter was ozonised according to [64], Under these conditions, a mixture of C-12 epimeric bisnorlabdanic oxidoketones (85) has been formed in a high yield. Its oxidation with monoperphtalic acid afforded a mixture of acetoxy oxides (75), from which acetic acid has been eliminated to give the unsaturated oxide (76). The latter was ozonised and the ozonolysis products were reduced with NaBffr into the diol (41). This four-step synthesis led to the diol (41) in an overall 44% yield (Scheme 14). 

DCCI = dicyclohexylcarbodiimide, EEDQ = l-ethoxycarbonyl-2-ethoxy-l, 2-dihydroquin-oline, DEAD = diethyl azodicarboxylate, MPP=monoperphtalic acid, TEA = trifluoro-acetic acid, TEA = triethylamine, Py = pyridine, Z = benzyloxycarbonyl, trOC = trichloro-ethoxycarbonyl, Su = succinimidyl, PNP =p-nitrophenyl, Pr=propyl, Bu = butyl, He = hexyl, Ph = phenyl, Bzl = benzyl, p-HO-Bzl = p-hydroxybenzyl and other acc. lUPAC rules. 

This method was introduced by Polonski and Chimiak 192,193) in 1974 (Scheme 47). It is based on the oxidation of Schiff bases (239) to appropriate oxaziridines (240) in ether using monoperphtalic acid (MPP). Bases (239) are obtained from esters of amino acids and anisyl aldehyde (238) and are oxidised without isolation. Oxaziridines (240) are next hydrolyzed with hydrochloric acid to N-hydroxyamino acids (1) or give p-toluenesulfonates of (76, 213), which crystallize readily, by splitting with hydroxylamine j7-toluenesulfonates in alcohol. Use of benzaldehyde is unfavourable and leads to nitrones. Use of mono-perphthalic acid permits one to follow the progress of the reaction due to precipitation of phthalic acid. This method is general. Because bases (239) racemize only very slowly it is possible to obtain 193) optically active compounds (1,76, 213). 

Oxidation of humulone with monoperphtalic acid gives in 75% yield compound 57 (Fig. 28) with melting point 65-68°C and molecular formula C21H32O3 (49). Further... 

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