Abstract
A synthetic approach directed towards the total synthesis of the novel protoilludane sesquiterpene pteridanone, the aglycon of the glucoside pteridanoside from a bioactive hot-water extract of the neotropical braken fern Pteridium aquilinum var. caudatum (Dennstaedtiaceae), has been delineated. This endeavour has delivered an advanced pre-target having the complete protoilludane skeleton with strategic placement of the functionalities and set the stage for the total synthesis of the natural product. The key features of our approach are the ready availability of the starting material (1,5-cyclooctadiene), an interesting photochemical [2+2]-cycloaddition and a thallium(III) mediated ring expansion reaction.
Highlights
Nature exhibits special flair for creating a vast array of carbocyclic skeleta with different concatenation of rings, replete with multitude of functionalities and stereochemical intricacies, among sesquiterpenoids.[1]
The isolation of sesquiterpenes from many diverse and exotic sources in recent years and observation of wide ranging biological activity in many of them has further added to their synthetic appeal
Protoilludyl cation 3, derived from farnesyl pyrophosphate 1 via the humulenyl cation 2 is a common precursor of a diverse range of sesquiterpene skeleta bearing a variegated union of 3, 4, 5 and 6-membered rings
Summary
Nature exhibits special flair for creating a vast array of carbocyclic skeleta with different concatenation of rings, replete with multitude of functionalities and stereochemical intricacies, among sesquiterpenoids.[1]. The hydroxy group in was protected and the derived acetate was treated with IBX to effect one step dehydrogenation as described recently by Nicolaou et al.[7] to furnish the enone in excellent yield, Scheme 3. The carbonyl group in the tricyclic ketones was protected as the 2,2-dimethyl-1,3-propylene ketal and further eliminative dehalogenation[8] furnished the cyclobutene compound in good yield.
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