3 research outputs found
Oxyanionic Sigmatropic Rearrangements Relevant to Cyclooctadienone Formation in Penostatins I and F
The results of several experiments designed to probe the energetic viability of a reaction path for generation of penostatins I (<b>3</b>) and F (<b>4</b>) via spontaneous [3,3]-sigmatropic rearrangement are reported. In particular, the enolate derived from the 2-vinyl-6-acyldihydropyran <b>8-cis</b> gave cyclooctadienone <b>12</b> via facile anionic oxy-Claisen rearrangement, demonstrating the feasibility of such an event
Case Study of Empirical and Computational Chemical Shift Analyses: Reassignment of the Relative Configuration of Phomopsichalasin to That of Diaporthichalasin
Phomopsichalasin was isolated and assigned structure <b>1</b> over 15 years ago. Analysis of its proton NMR data led us
to hypothesize
that not all aspects of the relative configuration of this structure
were correct. We have used both empirical and computational methods
to propose an alternative structure. Diaporthichalasin was reported
several years ago, and its structure was assigned as <b>7</b>, a diastereomer of structure <b>1</b>, and confirmed by a
single-crystal X-ray study. We have shown that diaporthichalasin and
phomopsichalasin are identical; that is, both have structure <b>7</b>. Additional aspects of NMR interpretation that provide guidance
for avoiding some of the pitfalls that can lead to incorrect structure
assignments are discussed. These recommendations/reminders include
(i) the use of complementary solvents for acquiring NMR data that
break accidental chemical shift degeneracy, (ii) the importance of
assigning coupling constants as extensively as possible, and (iii)
exercising caution when interpreting correlations in 2D spectra where
overlapping resonances are involved
Nucleophilic Deoxyfluorination of Phenols via Aryl Fluorosulfonate Intermediates
This
report describes a method for the deoxyfluorination of phenols
with sulfuryl fluoride (SO<sub>2</sub>F<sub>2</sub>) and tetramethylammonium
fluoride (NMe<sub>4</sub>F) via aryl fluorosulfonate (ArOFs) intermediates.
We first demonstrate that the reaction of ArOFs with NMe<sub>4</sub>F proceeds under mild conditions (often at room temperature) to afford
a broad range of electronically diverse and functional group-rich
aryl fluoride products. This transformation was then translated to
a one-pot conversion of phenols to aryl fluorides using the combination
of SO<sub>2</sub>F<sub>2</sub> and NMe<sub>4</sub>F. Ab initio calculations
suggest that carbon–fluorine bond formation proceeds via a
concerted transition state rather than a discrete Meisenheimer intermediate