The 125thAnniversary of the Tröger's Base Molecule: Synthesis and Applications of Tröger's Base Analogues

Asymmetric synthesis of N-stereogenic molecules: diastereoselective double aza-Michael reaction

A novel approach towards the asymmetric synthesis of N-stereogenic molecules via double aza-Michael addition was developed. The diastereomeric ratio can be increased by a thermodynamically controlled isomerization mechanism. Simple separation and functionalization of the products afford N-stereogenic compounds in high enantiomeric purity.

Tröger's base quasiracemates and crystal packing tendencies

A family of 7 Tröger's base (TB) compounds that vary in configuration (quasiracemates, racemates, and enantiomers) and chemical substitutions (Me, Cl, and Br) has been investigated.

Facile access to imidazole and imidazolium substituted dibenzo-diazocines

The C₂-symmetrical 2,8- and 4,10-diimidazo methano dibenzo diazocines were synthesized and converted into alkyl imidazolium salts.

Modular Synthesis of Optically Active Tröger's Base Analogues

For the first time, enantioselective catalysis was applied for the preparation of Tröger's base derivatives affording N-stereogenic building blocks not only in excellent enantiomeric purity but also in an easily scalable fashion. Enzymatic kinetic resolution proved efficient to yield functionalized Tröger's bases, which can be subsequently modified by various chemical methods without any erosion of stereogenic information. In concert with a preparatively convenient protocol for the synthesis of the racemic substrates from commercially available anilines, a highly practicable and flexible route towards a wide range of enantiopure Tröger's base analogues is provided.

Readily accessible chiral at nitrogen cage structures

The reaction of glycine-N-methyl amide with paraformaldehyde in the presence of ytterbium triflate (1 mol%) leads to a novel cage structure 6 which is chiral at nitrogen. Single crystal X-ray analysis and DFT calculations suggest this cage structure is rigid and adopts a single low energy conformation. Use of single enantiomer α-amino amides results in two diastereomeric tertiary amines that differ in their absolute configuration at nitrogen. These diastereoisomers interconvert under acidic conditions but are configurationally stable under basic conditions and can be readily separated by either crystallisation or column chromatography. By reacting racemic chiral α-amino amides a third diastereomeric cage can also be isolated through this reaction protocol. Preparation of mixed cages by reacting two different α-amino amides is also possible allowing for greater structural diversity in the products to be attained. Preliminary mechanistic studies show that all three methylene units in the cage structure are labile and can be replaced under acidic reaction conditions.