Chun Y, Remmerswaal WA, Codée JDC, Woerpel KA. Neighboring-Group Participation by C-2 Acyloxy Groups: Influence of the Nucleophile and Acyl Group on the Stereochemical Outcome of Acetal Substitution Reactions.
Chemistry 2023;
29:e202301894. [PMID:
37410662 PMCID:
PMC10592418 DOI:
10.1002/chem.202301894]
[Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 07/06/2023] [Accepted: 07/06/2023] [Indexed: 07/08/2023]
Abstract
A single acyloxy group at C-2 can control the outcome of nucleophilic substitution reactions of pyran-derived acetals, but the extent of the neighboring-group participation depends on a number of factors. We show here that neighboring-group participation does not necessarily control the stereochemical outcome of acetal substitution reactions with weak nucleophiles. The 1,2-trans selectivity increased with increasing reactivity of the incoming nucleophile. This trend suggests the intermediacy of both cis-fused dioxolenium ions and oxocarbenium ions in the stereochemistry-determining step. In addition, as the electron-donating ability of the neighboring group decreased, the preference for the 1,2-trans products increased. Computational studies show how the barriers for the ring-opening reaction on the dioxolenium ions and the transition states to provide the oxocarbenium ions change with the electron-donating capacity of the C-2-acyloxy group and the reactivity of the nucleophile.
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