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J Org Chem. 2019 Jan 4;84(1):273-281. doi: 10.1021/acs.joc.8b02603. Epub 2018 Dec 19.

π-Facial Selectivities in Hydride Reductions of Hindered Endocyclic Iminium Ions.

Author information

1
Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095-1569 , United States.
2
Department of Chemistry , Yale University , New Haven , Connecticut 06520 , United States.

Abstract

The origins of π-facial selectivities in the borohydride reduction of endocyclic iminium ions have been elucidated by density functional theory calculations. In reductions of conjugated ("thermodynamic") iminium ions, the π-facial preference of the hydride attack was found to be due to torsional steering. Attack at the favored π-face leads to a lower-energy "half-chair"-like conformation of the tetrahydropyridine product, whereas attack at the other π-face results in an unfavorable "twist-boat" conformation. In reductions of nonconjugated ("kinetic") iminium ions, torsional distinction is small between the top- and bottom-face attacks, and the π-facial selectivity of the hydride approach is primarily due to steric hindrance.

PMID:
30516383
PMCID:
PMC6467781
[Available on 2020-01-04]
DOI:
10.1021/acs.joc.8b02603

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