Computational Modeling of the Feasibility of Substituted [1.1.1]Propellane Formation from Anionic Bridgehead Bromide Precursors

Abstract

[1.1.1]Propellane, a compound whose structure includes two saturated carbons in which all four bonds are directed into a single hemisphere, is of theoretical interest, but has also seen recent practical applications. Mono-, di-, and trisubstituted derivatives of this propellane (by substitution of its CH2 bridges with O, S, NH, CF2, CO, SO, and SO2) remain unknown despite several computational studies that have suggested some may be stable. In this study, we show that, in several cases, substituted propellanes are spontaneously formed upon the attempted computational optimization of the geometries of anionic bridgehead bromide precursors using the ωB97X-D/aug-cc-pVDZ DFT method. Spontaneous formation suggests that these propellanes are at lower energy relative to the precursors and, therefore, are promising synthetic targets. The success or failure to spontaneously form the propellane is considered in relation to the length and strain energy of the central bridgehead-bridgehead bond, as well as the total strain energy of each propellane.