The (±)-6-Aza[1.0]triblattane Skeleton: Contraction beyond the Wilder-Culberson Ring System

The (±)-5-Aza[1.0]triblattane Skeleton via Azetine Cycloaddition

The first synthesis of the 5-aza[1.0]triblattane skeleton was achieved through a [4 + 2] cycloaddition approach using a suitably protected azetine and cyclopentadiene. A series of azetines were synthesized to explore both stability and suitable N-protection. The key step following cycloaddition utilized a noninitiated protonated aminyl radical cyclization to install the final 5-azatriblattane bond, but it was found to be considerably more unstable than the 6-aza isomer under acidic conditions.

9-Azahomocubane

Homocubane, a highly strained cage hydrocarbon, contains two very different positions for the introduction of a nitrogen atom into the skeleton, e. g., a position 1 exchange results in a tertiary amine whereas position 9 yields a secondary amine. Herein reported is the synthesis of 9-azahomocubane along with associated structural characterization, physical property analysis and chemical reactivity. Not only is 9-azahomocubane readily synthesized, and found to be stable as predicted, the basicity of the secondary amine was observed to be significantly lower than the structurally related azabicyclo[2.2.1]heptane, although similar to 1-azahomocubane.

Seeking the most stable isomer of azahomocubanes

This study examines the stability and protonation properties of four potential azahomocubanes. Through high-level ab initio computations, we find that 9-azahomocubane is the most stable isomer, closely followed by 5-azahomocubane, 1-azahomocubane, and 2-azahomocubane. However, understanding the stability of the systems with a nitrogen atom incorporated into a highly constrained polycyclic environment extends beyond mere bond angles or hybridization considerations. Strain energy analysis reveals that azahomocubanes experience less strain compared to their carbon congeners. An exploration of multiple solvents shows that their impact on relative energies and geometries is negligible. On the other hand, among the four isomers, 2-azahomocubane exhibits the highest tendency for protonation. Basicity, as assessed through the minimum electrostatic potential, correlates well with protonation affinities.

seco-1-Azacubane-2-carboxylic acid-Amide Bond Comparison to Proline

seco-1-Azacubane-2-carboxylic acid, an unusual and sterically constrained amino acid, was found to undergo amide bond formation at both the N- and C-termini using proline based bioactive molecule templates as a concept platform.

1-Azahomocubane

Highly strained cage hydrocarbons have long stood as fundamental molecules to explore the limits of chemical stability and reactivity, probe physical properties, and more recently as bioactive molecules and in materials discovery. Interestingly, the nitrogenous congeners have attracted much less attention. Previously absent from the literature, azahomocubanes, offer an opportunity to investigate the effects of a nitrogen atom when incorporated into a highly constrained polycyclic environment. Herein disclosed is the synthesis of 1-azahomocubane, accompanied by comprehensive structural characterization, physical property analysis and chemical reactivity. These data support the conclusion that nitrogen is remarkably well tolerated in a highly strained environment.