Studies in sigmatropic rearrangements of N-prenylindole derivatives - A formal enantiomerically pure synthesis of tryprostatin B

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Abstract

Rearrangement of Na-prenyl-Nb-acetyltryptamine, induced by BF3·Et2O at low temperature, leads to a 2-prenyl derivative, and thence to the tricyclic tryptamine 7 and the indoline 8. Similarly, Na-prenyl-Nb-phthaloyl-l-tryptophan methyl ester furnished the corresponding 2-prenyl derivative 16, a known advanced precursor of tryprostatin B. Density functional (B3LYP) calculations for the putative rearrangement transition state for N-prenylskatole show that prior coordination of BF3 to the indolic nitrogen changes the character of the subsequent sigmatropic pericyclic shifts from being entirely covalent to acquiring a significant degree of ionic character. The shifting prenyl group favours the endo over the exo mode of the transition state by 4.1 kcal mol -1.

Original languageEnglish
Pages (from-to)3966-3972
Number of pages7
JournalOrganic & Biomolecular Chemistry
Volume4
Issue number21
DOIs
Publication statusPublished - 25 Oct 2006

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