A computational study of anionic alkoxide–allene and amide–allene cyclizations

Cumine, Florimond and Young, Allan and Reissig, Hans-Ulrich and Tuttle, Tell and Murphy, John A. (2017) A computational study of anionic alkoxide–allene and amide–allene cyclizations. European Journal of Organic Chemistry, 2017 (46). pp. 6867-6871. ISSN 1434-193X (https://doi.org/10.1002/ejoc.201701381)

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Computational studies have been performed on potassium alkoxide-allenes, as well as potassium and lithium amido-allenes to probe the mechanism of their cyclizations to dihydrofurans and to 2,5-dihydropyrroles. A long-standing proposal envisaged electron transfer from dimsyl anions (formed by deprotonation of the solvent DMSO) but this pathway shows an exceptionally high kinetic barrier, while direct 5-endo-trig cyclization of the alkoxides and amides is much more easily achievable. The energy profiles for 4-exo-trig cyclizations onto the allenes are also explored, and the preferred formation of the observed five-membered products is rationalized.