One-Pot Synthesis of Spirocyclopenta[a]indene Derivatives via a Cascade Ring Expansion and Intramolecular Friedel–Crafts-Type Cyclization

A one-pot efficient synthetic approach for the rapid construction of spirocyclopenta­[a]­indene derivatives has been developed via an iodine-initiated cascade ring expansion and intramolecular Friedel–Crafts-type cyclization from propargyl alcohol-tethered alkylidenecyclobutanes under mild conditions with broad substrate scope. This cascade process can be elegantly conducted on a gram scale. A plausible reaction mechanism has been proposed on the basis of a series of deuterium labeling and control experiments.本研究开发了一种一锅法高效合成策略，可在温和条件下，以连有炔丙醇基团的亚甲基环丁烷类化合物为底物，通过碘引发的级联扩环与分子内傅-克（Friedel–Crafts）型环化反应，快速构建螺环戊并[a]茚衍生物，该策略具备宽泛的底物适用范围。该级联过程可顺利放大至克级规模进行。基于一系列氘代标记实验与对照实验，本研究提出了合理的反应机理。