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

ABSTRACT: The origins of ?-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 ?-facial preference of the hydride attack was found to be due to torsional steering. Attack at the favored ?-face leads to a lower-energy "half-chair"-like conformation of the tetrahydropyridine product, whereas attack at the other ?-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 ?-facial selectivity of the hydride approach is primarily due to steric hindrance.

SUBMITTER: Chen S

PROVIDER: S-EPMC6467781 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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

Chen Shuming S Chan Amy Y AY Walker Morgan M MM Ellman Jonathan A JA Houk K N KN

The Journal of organic chemistry 20181219 1

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" ...[more]

PMID: 30516383

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