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Updated: May 3, 2026
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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
The Many Faces of (R*)-4-[(S*)-1-Methanesulfonyloxypropyl]-3-methoxy-1,3-oxazinane
Robert A Pascal1, Sarah A Neuenswander2, Justin T Douglas2
1Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, USA.
Abstract:
The 1H NMR spectrum of (R*)-4-[(S*)-1-methanesulfonyloxypropyl]-3-methoxy-1,3-oxazinane (3) is incomprehensible at room temperature due to line broadening from the dynamic exchange of many conformations. VT-NMR studies show two equal populations at low temperatures. As the temperature increases, they coalesce into a single population with a free energy of activation for this process of 14.0-14.6 kcal/mol. DFT studies indicate that each of the low-temperature populations is a collection of rapidly interconverting species, and the critical barrier to interconversion is an inversion at nitrogen in compound 3 with calculated barriers of 14.3-16.0 kcal/mol, depending on the computational method employed.
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