Studies in sigmatropic rearrangements of N-prenylindole derivatives ? a formal enantiomerically pure synthesis of tryprostatin B
作者:A. Sofia P. Cardoso、M. Manuel B. Marques、Natarajan Srinivasan、Sundaresan Prabhakar、Ana M. Lobo、Henry S. Rzepa
DOI:10.1039/b606457d
日期:——
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 molâ1.
Na-异戊二烯基-Nb-乙酰色胺在低温下由BF3·Et2O诱导发生重排,生成2-异戊二烯基衍生物,进而生成三环色胺7和二氢吲哚8。类似地,Na-异戊二烯基-Nb-邻苯二甲酰基-L -色氨酸甲酯提供了相应的 2-异戊二烯基衍生物 16,这是一种已知的胰前列腺素 B 的高级前体。 N-异戊烯基粪臭素推定重排过渡态的密度泛函 (B3LYP) 计算表明,BF3 与吲哚氮的事先配位改变了特性随后的σ周环从完全共价转变为获得显着程度的离子特征。移动的异戊二烯基团有利于过渡态的内型模式,而不是外型模式,高出 4.1 kcal mol·1。