Optically Active Selenoxides: Structural and Synthetic Aspects

Abstract

Synthetic approaches to the preparation of non-racemic selenoxides and the problem of their optical stability are discussed in this mini review.

Asymmetric Allenylation of Alkynes mediated by Chiral Organoselenated Reagents under Oxidative Conditions

“…Results gathered from 4‐octyne thus undoubtedly show that both (R)‐ or (S)‐ enantiomerically‐enriched allenylamides 4 are accessible based on our capacity to separate a mixture of diastereomers featuring a highly stable absolute configuration at the selenium atom. It should be emphasized that such stability is unusual for enantioenriched selenoxides, which tend to racemize fairly quickly in presence of polar solvents or external nucleophiles via transient tetravalent intermediates [17] . Herein, as shown on Figure 1, selenoxides 17 are highly substituted.…”

“…It should be emphasized that such stability is unusual for enantioenriched selenoxides, which tend to racemize fairly quickly in presence of polar solvents or external nucleophiles via transient tetravalent intermediates. [17] Herein, as shown on Figure 1, selenoxides 17 are highly substituted. This feature most probably turns any Se-centered attack by external nucleophiles impossible, and thus this intrinsic well-organized steric hindrance might be acting as a protecting shield towards selenoxide epimerization.…”

“…The main challenge was thus to be able to reach high levels of enantioselectivities using chiral vinyl selenoxides that can β‐eliminate only at elevated temperature (Scheme 2). Indeed, as mentioned above, [10b,c,13] β‐elimination from vinyl selenoxides bearing non‐electron withdrawing substituents requires thermal activation; a feature that could be incompatible with a perfect conservation of the chirality at a selenoxide center [17] . Our goal was thus to design chiral selenium‐based reagents that could: 1‐ stabilize the absolute configuration of the selenium (IV) atom in order to, 2‐ promote a general reagent‐controlled diastereoselective vinyl selenoxide β‐ syn ‐elimination towards highly enantioenriched allenylamides (Scheme 2).…”