A Novel Approach to Functionalized Heterohelicenes via Chromium-Templated Benzannulation Reactions
作者:Karl Heinz Dötz、Jochen F. Schneider、Martin Nieger、Kalle Nättinen
DOI:10.1055/s-2005-861864
日期:——
A series of functionalized oxa- and thiaheterohelicenes has been prepared by a new progressive annulation technique based on the chromium-templated [3+2+1]benzannulation reaction of hetero[5]helicene carbene complexes with various alkynes partly in competition of angular and linear annulation. Oxidative work-up with CAN yields the respective quinones along with small amounts of nitrated products or a nitrate ester byproduct. Thermal recomplexation of an acylated monobenzannulation product by Cr(CO)6 affords the corresponding, thermodynamically favored η6-oxa[6]helicene-Cr(CO)3 complex. Bidirectional benzannulation reveals a more delicate regioselectivity and yields three different isomers including a bisquinone with an unprecedented bislinear annulation pattern. Molecular structures determined by X-ray analysis indicate a decreasing helical distortion as a result of progressive annulation, steric demand of the quinone substitution pattern (Ph>Pr>Et), or the nature of the embedded heterocycle (SO2>S>O).
通过一种新的渐进环化技术制备了一系列官能化的氧杂环己烯和噻杂环己烯,该技术基于杂[5]螺旋碳烯络合物与各种炔烃在部分角环化和线环化竞争中发生的铬引发的[3+2+1]苯环化反应。用 CAN 进行氧化处理,可得到相应的醌类化合物以及少量硝化产物或硝酸酯副产物。用 Cr(CO)6 对酰化的单苯并annulation 产物进行热再络合,可得到相应的、热力学上有利的 δ-6-氧杂[6]螺旋烯-Cr(CO)3络合物。双向苯annulation 揭示了一种更微妙的区域选择性,并产生了三种不同的异构体,包括一种具有前所未有的双线环化模式的双醌。通过 X 射线分析确定的分子结构表明,螺旋畸变因逐步环化、醌取代模式的立体需求(Ph>Pr>Et)或嵌入杂环的性质(SO2>S>O)而逐渐减小。