Synthesis of <i>Aristotelia</i>‐Type Alkaloids. Part XII. Total synthesis of (−)‐tasmanine. Stereoelectronic factors that control the rearrangement of 3<i>H</i>‐indol‐3‐ol derivatives to oxindoles ( = 1,3‐dihydro‐2<i>H</i>‐indol‐2‐ones) or to pseudoindoxyls ( =1,2‐dihydro‐3<i>H</i>‐indol‐3‐ones)

Abstract

Abstract The oxidative transformation of (+)‐aristoteline ((+)‐ 5 ) into its metabolites, the recently synthesized indole alkaloids (−)‐serratoline ((−)‐ 6 ), (+)‐aristotelone ((+)‐ 2 ), and (−)‐alloaristoteline ((−)‐ 22 ), was investigated in more detail. It was demonstrated that the diastereoface selectivity of the reaction of (+)‐ 5 with 3‐chloroperbenzoic acid can be altered by variation of the solvent as well as by addition of CF 3 COOH. The chemoselectivity of the 1,2‐rearrangement of the intermediate 3 H ‐indol‐3‐ol derivatives could be controlled as follows: treatment of 3 H ‐indol‐3‐ols with aqueous polyphosphoric acid led to the pseudoindoxyl ( = 1,2‐dihydro‐3 H ‐indol‐3‐one) derivatives, whereas an analogous treatment of the corresponding O ‐benzoates furnished exclusively the corresponding, constitutionally isomeric 2‐oxindole ( = 1,3‐dihydro‐2 H ‐indol‐2‐one) products. Exploitation of these and related findings led to efficient total syntheses of the Aristotelia alkaloid (−)‐tasmanine ((−)‐ 1 ) and of the corresponding unnatural epimer (+)‐ 12 , as well as of the two pseudoindoxyls (+)‐aristotelone ((+)‐ 2 ) and (−)‐2‐epiaristotelone ((−)‐ 11 ). All these transformations were carried out with synthetic (+)‐aristoteline ((+)‐ 5 ) as the single indole alkaloid precursor.