DABCO-based ionic salts: synthesis, characterization, and application as organocatalysts in asymmetric reduction reactions

Abstract

GUMBOS (group of uniform materials based on organic salts) are highly functional and tunable organic ionic materials that exhibit a solid state at room temperature, composed of oppositely charged bulky ions with high thermal stability. A variety of GUMBOS has been designed and synthesized by selecting appropriate ion pairs to use in targeted applications of different fields. Herein, parent DABCO-based GUMBOS were synthesized from the reaction of terpene such as (-)-menthol or (-)-borneol or (+)-fenchol and chloroacetic acid followed by DABCO. To formulate GUMBOS derivatives, the parent salt (with chloride counter-anion) was modified through an anion exchange metathesis process by taking different sodium/potassium salts. Structure elucidation was done through NMR, polarimeter, TGA, and GC-MS techniques. The synthesized ionic species were employed as organocatalysts in the enantioselective reduction reactions of various prochiral ketones to chiral alcohols. Low to good enantiomeric excess was obtained.

Graphical Abstract

The easily available and low-cost parent compounds i.e., terpenes and DABCO were used for the synthesis of GUMBOS through facile and simple synthetic routes. The salts were obtained with good yield, possessed optical activity, and had high thermal stability. Further, the organocatalytic role of salts was studied in asymmetric reduction reactions.