Accessing an Extreme Steric Regime of C–O Atropisomerism through Overcrowded Iodane-Mediated Rearrangement
Abstract
C–O atropisomerism in aryl ethers is intrinsically difficult to stabilize because oxygen provides limited steric leverage and the two C–O bonds may undergo concerted rotation (gearing). Here, we report that the reaction of an overcrowded (diacetoxyiodo)arene with cyclic 1,3-diketones generates aryliodonium ylides that undergo spontaneous rearrangement to furnish highly congested atropisomeric aryl vinyl ethers. These compounds occupy a previously unexplored steric regime of C–O atropisomerism and display configurational stability that strongly depends on the cyclic 1,3-diketone framework. Whereas the cyclopentane-1,3-dione derivative exhibits an enantiomerization barrier of 32.9 kcal mol–1, the corresponding cyclohexane-1,3-dione and dimedone derivatives reach barriers approaching 40 kcal mol–1. The alkenyl C–I bond serves as both a major contributor to atropostability and a synthetic handle for systematic modulation of the enantiomerization barrier through deiodination and cross-coupling. Computational studies revealed a striking energetic separation between gearing and enantiomerization. Even in this extreme steric regime, gearing remains accessible with barriers of ~15 kcal mol–1 and is only weakly affected by the iodine substituent, whereas enantiomerization requires substantially higher-energy rotational pathways. These findings provide a mechanistic picture of molecular motion under extreme steric constraints and establish overcrowded iodanemediated rearrangement as a route to previously inaccessible C–O atropisomeric architectures.
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BibTeX
@misc{li2026accessing,
title = {{Accessing an Extreme Steric Regime of C–O Atropisomerism through Overcrowded Iodane-Mediated Rearrangement}},
author = {Bin Li and Jun Kikuchi and Arimasa Matsumoto and Naohiko Yoshikai},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15009250/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009250/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Accessing an Extreme Steric Regime of C–O Atropisomerism through Overcrowded Iodane-Mediated Rearrangement
AU - Bin Li
AU - Jun Kikuchi
AU - Arimasa Matsumoto
AU - Naohiko Yoshikai
PY - 2026
DA - 2026/09/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15009250/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15009250/v1
AB - C–O atropisomerism in aryl ethers is intrinsically difficult to stabilize because oxygen provides limited steric leverage and the two C–O bonds may undergo concerted rotation (gearing). Here, we report that the reaction of an overcrowded (diacetoxyiodo)arene with cyclic 1,3-diketones generates aryliodonium ylides that undergo spontaneous rearrangement to furnish highly congested atropisomeric aryl vinyl ethers. These compounds occupy a previously unexplored steric regime of C–O atropisomerism and display configurational stability that strongly depends on the cyclic 1,3-diketone framework. Whereas the cyclopentane-1,3-dione derivative exhibits an enantiomerization barrier of 32.9 kcal mol–1, the corresponding cyclohexane-1,3-dione and dimedone derivatives reach barriers approaching 40 kcal mol–1. The alkenyl C–I bond serves as both a major contributor to atropostability and a synthetic handle for systematic modulation of the enantiomerization barrier through deiodination and cross-coupling. Computational studies revealed a striking energetic separation between gearing and enantiomerization. Even in this extreme steric regime, gearing remains accessible with barriers of ~15 kcal mol–1 and is only weakly affected by the iodine substituent, whereas enantiomerization requires substantially higher-energy rotational pathways. These findings provide a mechanistic picture of molecular motion under extreme steric constraints and establish overcrowded iodanemediated rearrangement as a route to previously inaccessible C–O atropisomeric architectures.
ER -