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 (SO₂F₂) and tetramethylammonium fluoride (NMe₄F) via aryl fluorosulfonate (ArOFs) intermediates. We first demonstrate that the reaction of ArOFs with NMe₄F 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 SO₂F₂ and NMe₄F. Ab initio calculations suggest that carbon–fluorine bond formation proceeds via a concerted transition state rather than a discrete Meisenheimer intermediate