Benzeneselininic anhydride

Chaparrinone (40a) which possesses most of the structural requirements for in vivo antileukemic activity in the PS test system but lacks an ester side chain at C-15 and/or at C-6, does not display any significant antineoplastic activity. In a search for direct methods of quassinoid functionalization benzeneselininic anhydride (84) was considered as a possible reagent for the introduction of a double bond in the lactonic ring of chaparrinone (40 a) (41). 

Chaparrinone triacetate (86) on reaction with benzeneselininic anhydride afforded the desired A " -dehydro compound (87). In addition, two other products (88) and (89) arising, interestingly enough, from angular hydroxylation at C-5, were isolated. Deacetylation of these three products gave the free alcohols (90), (91) and (92) which however did not show any significant activity. Further preliminary experiments to introduce an oxygen function at C-15 remained unsuccessful. 

The mechanism proposed for the observed angular hydroxylation is outlined in Scheme 2. Enolisation of the 2-keto group of chaparrinone triacetate (86) is followed by attack of benzeneselininic anhydride at C-3 of the enol. This mechanism explains both the position and the configuration of the new OH-group. 

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See also in sourсe #XX -- [ , ]

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