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One-pot organocatalyzed synthesis of tricyclic indolizines

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Indolizines and their saturated derivatives are important structural motifs present in several biologically active compounds of both natural and synthetic origin. We describe herein a one-pot approach for the synthesis of tricyclic indolizines catalyzed by a bicyclic imidazole-alcohol. The protocol is based on an aqueous Morita-Baylis-Hillman reaction between pyridine-2-carboxaldehydes and six- or seven-membered cyclic enones, followed by sequential intramolecular cyclization and dehydration. So, in a single operational step two new bonds (C-C and C-N) are formed in an organocatalyzed process that takes place in simple conditions (stirring in water at 60 °C for 12 h) and with great atom economy (water as the sole byproduct), affording the purified compounds in yields ranging from 19 to 70%. The facility of the cyclization strongly depends on the size of the cycloalkenone ring: while MBH adducts derived from six-, seven- or eight-membered cycloenones are readily transformed into the corresponding indolizines, cyclopentenone-derived MBH adducts do not cyclize. A competition experiment revealed that cycloheptenone- derived MBH adducts cyclize faster than cyclohexenone-derived adducts. Model DFT calculations have been performed to rationalize these reactivity trends.

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Organic & Biomolecular Chemistry, 2023, vol. 17, p. 1-15

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Articles publicats en revistes (Ciència dels Materials i Química Física)

# metadata.dc.title[].value
One-pot organocatalyzed synthesis of tricyclic indolizines