Hyperpyramidalized alkenes with bond orders near 1.5 as synthetic building blocks

TL;DR

This paper explores unusual alkenes with distorted geometries and bond orders near 1.5, using them to create new chemical structures.

Contribution

The study introduces hyperpyramidalized alkenes as novel synthetic building blocks with unique reactivity.

Findings

Hyperpyramidalized alkenes have bond orders approaching 1.5 due to weak π-bonding.

Cubene and 1,7-quadricyclene were successfully used in cycloadditions to form complex molecular scaffolds.

Abstract

Alkenes typically have trigonal planar geometries at each terminus, with favourable σ- and π-bonding leading to a bond order of ~2. Here we consider unusual alkenes that possess an extreme form of geometric distortion, termed hyperpyramidalization. In a hyperpyramidalized alkene, geometries deviate remarkably from the typical trigonal planar alkene geometry, leading to weak π-bonding and abnormal alkene bond orders approaching 1.5. Cubene and 1,7-quadricyclene, first validated in 1988 and 1979, respectively, but overlooked for decades since, are the focus of the present study. We leverage their unusually weak π-bonds in cycloadditions, enabling the construction of complex scaffolds and access to previously unrealized chemical space. The origins of the unusually low bond orders were investigated using computational methods. These efforts are expected to prompt future studies of molecules that display hyperpyramidalization or atypical bond orders.

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