An in situ infrared spectroscopic investigation of the rh-catalyzed [5+1+2+1] cycloaddition reaction of vinylcyclopropanes, terminal alkynes, and carbon monoxide

Abstract

In the [5+1+2+1] cycloaddition reaction, hydroxydihydroindanones can be synthesized from vinylcyclopropanes and alkynes under a carbon monoxide atmosphere to produce five new C-C bonds in a single step. Dihydroindanones are typically produced through reduction of indenones. However, since various multistep methods are used to obtain indenones, the single step [5+1+2+1] cycloaddition reaction provides an attractive, alternative synthetic route. The vinylcyclopropane (VCP) starting material has been successfully prepared through modification of a previously reported 3-step synthetic method. The [5+1+2+1] cycloaddition reaction reported by Wender et al. was tested and confirmed to work with the synthesized VCP, as crystals of the desired hydroxydihydroindanone cycloaddition product were obtained. In situ infrared spectroscopic studies of the cycloaddition reaction were performed. Although these studies were unsuccessful in identifying reaction intermediates of the cycloaddition pathway, second derivative analysis of the spectroscopic data successfully resolved overlapping CO peaks. The experimentally obtained spectra of the reaction solution could not be compared to theoretical pure spectra of components believed to be in solution, as the IR frequency calculations (performed using the functional and basis set needed to apply a reported vibrational scaling factor) failed to converge to a minimum. Finally, a DFT investigation of the monometallic and bimetallic cycloaddition pathways was performed. This investigation suggested that the bimetallic pathway is both kinetically and thermodynamically favourable, which is inconsistent with previous experimental results.