Synthesis of 3,4-dihydropyran-2-ones
Ring-closing metathesis of unsaturated carboxylic acids vinyl esters enables an efficient synthesis of endocyclic enol lactones. The developed methodology offers an easy route for synthetically challenging target molecules with different functional groups and substitution. Vinyl esters of cyclic carboxylic acids can also be successfully applied for domino ring-opening ring-closing metathesis sequences.
A. Brodzka, F. Borys, D. Koszelewski, R. Ostaszewski, J. Org. Chem., 2018, 83, 8655-8661.
After NHC-catalyzed activation of acetic esters, the catalytically generated triazolium enolate intermediates serve as two-carbon nucleophiles that undergo highly enantioselective reactions with enones and α,β-unsaturated imines to give α-unsubstituted δ-lactones and lactams, respectively.
S. Chen, L. Hao, Y. Zhang, B. Tiwari, Y. R. Chi, Org. Lett., 2013, 15, 5822-5825.
An N-Heterocyclic carbene (NHC)-catalyzed highly enantioselective lactonization of modified enals with enolizable aldehydes proceeds via α,β-unsaturated acylazolium intermediates and yields synthetically important 4,5-disubstituted dihydropyranones.
S. R. Yetra, T. Kaicharla, S. S. Kunte, R. G. Gonnade, A. T. Biju, Org. Lett., 2013, 15, 5202-5205.
Asymmetric Michael addition-lactonization reactions of β,γ-unsaturated α-keto esters with thioesters catalyzed by a proline-derived urea provide 3,4-dihydropyranones and spiro-3,4-dihydrocoumarin-fused 3′,4′-dihydropyranones in high yield with excellent stereoselectivities via bioinspired S-to-O acyl-transfer reactions.
H. Jin, J. Lee, H. Shi, J. Y. Lee, E. J. Yoo, C. E. Song, D. H. Ryu, Org. Lett., 2018, 20, 1584-15888.