Amberlyst-15 catalysed retro-Claisen condensation of beta-diketones with alcohols: A practical approach to synthesize esters and ketoesters

Esters are fundamental class of organic compounds with tremendous industrial applications. They are generally synthesized via the condensation of alcohol with acid. Herein, we report synthesis of esters and keto esters via retro-Claisen condensation of alcohols with ss-diketones in presence of Amberlyst-15, a commercially available heterogeneous catalyst. The methodology is applied to synthesize several industrially relevant acetates, such as n-butyl acetate, isobutyl acetate, 2-ethylhexyl acetate and isopropyl acetate in multi-gram scale. When 2-acetyl cyclohexanone or 2-acetyl cyclopentanone were used as ss-diketones, long chain keto-esters formed as sole products in excellent yields. The reaction tolerates a wide range of functional groups, such as olefins, alkynes, halides, nitro and esters. Furthermore, the protocol allows late-stage acetylation of naturally occurring alcohols. The methodology provides a practical approach for large scale synthesis of esters using fixed-bed continuous process. The catalyst can be recovered from the reaction mixture and reused up to 5 cycles without significant change in catalytic activity. To the best of our knowledge, this is the first example of a reusable Bronsted acid catalyst used in the synthesis of esters via retro-Claisen type condensation of alcohols and ss-diketones.

Automated summary

The synthesis of esters and keto esters via retro-Claisen condensation of alcohols with ss-diketones in the presence of a commercially available heterogeneous catalyst, Amberlyst-15, was reported. Several industrially relevant acetates were synthesized in multi-gram scale, and long chain keto-esters were obtained in excellent yields. The protocol allows for a practical approach for large scale ester synthesis and the catalyst can be reused for multiple cycles.