On the Transfer of Chirality, Thermodynamic Stability, and Folding Characteristics of Stereoisomeric Gated Baskets

• Published in: European journal of organic chemistry 2015-11, Vol.2015 (31), p.6832-6840
• Main Authors: Hu, Lei, Polen, Shane, Hardin, Alex M., Pratumyot, Yaowalak, Hadad, Christopher M., Badjić, Jovica D.
• Format: Article
• Language: English
• Subjects: Cavitands; Chirality; Host-guest chemistry; Supramolecular chemistry
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201501071

We have prepared and characterized chiral and gated baskets (P/M)‐2, each containing a twisted P or M platform and three amidopyridine gates at the rim. Racemic (P/M)‐2 was found (1H NMR and IR spectroscopy) to stay monomeric in CDCl3 at 298.0 K with the gates forming a seam of intramolecular N–H···N hydrogen bonds. In particular, the amidopyridine gates assume a unidirectional orientation, as directed by the twisted platform, that is, the P‐shaped cup sets the amidopyridine gates in a counterclockwise (–) orientation of intramolecular N–H···N hydrogen bonds (VT 1H/13C NMR and M06‐2X/6‐31G*). The folded form of spacious (355 Å3) and chiral (P/M)‐2 undergoes an unfolding process in the presence of the polar [D6]DMSO solvent; specifically, with around 25 vol.‐% of [D6]DMSO, the N–H···N hydrogen bonds at the rim are broken, thereby allowing a stochastic rotation of the amidopyridine gates about the rim. Interestingly, the thermal stability of folded (P/M)‐2 is good with only a small fraction of unfolded state(s) forming at 104 °C in o‐xylene. We have obtained stereoisomeric and gated baskets comprising a P or M twisted cup and amidopyridine gates at the rim. The gates form a seam of intramolecular hydrogen bonds to occlude space. They also assume a unidirectional orientation, induced by the cup's shape. Chemical and thermal stimuli trigger the basket's unfolding, which could be used in the design of switchable sensors and catalysts.