Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 39, Pages 21272-21276Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202108258
Keywords
Bronsted acid catalysis; cycloaddition; cyclopropane; isobenzopyryliums; strained molecules
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Funding
- National Natural Science Foundation of China [91956114, 22071210]
- Hong Kong Research Grants Council [16302318, 16303420]
- Innovation and Technology Commission [ITC-CNERC14SC01]
- Changzhou SciTech Program [CJ20200082]
- Natural Science Foundation of the Jiangsu Higher Education Institutions of China [20KJB150012]
- Jiangsu specially appointed professors program
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This study presents a new method for accessing cyclopropanes embedded in a polycyclic bridged architecture through a mild intermolecular convergent process. Unlike conventional approaches, this protocol does not require highly active carbenoid intermediates or strong conditions. The key cyclopropane ring is formed between the well-positioned nucleophile and electrophile in the adduct, showing a new reactivity of the versatile isobenzopyryliums.
Cyclopropanes embedded in a polycyclic bridged architecture are a versatile structural motif, but such complex frameworks often impose substantial synthetic challenges. Herein we introduce a new approach for the expedient access to such spring-loaded strained systems via an exceptionally mild intermolecular convergent process between the readily available isobenzopyryliums and vinyl boronic acids. Different from the typical conventional approaches, our protocol does not involve the highly active carbenoid intermediates or strong conditions in order to overcome the disfavored kinetic and thermodynamic problems. Instead, the key cyclopropane ring was formed between the well-positioned nucleophile and electrophile in the adduct from the regioselective [4+2] cycloaddition. Thus, this unusual process also represents a new reactivity of the versatile isobenzopyryliums. The choice of a Bronsted acid catalyst with proper acidity is crucial to the high efficiency and selectivity for this multiple bond-forming process. The strained products are precursors to other useful synthetic building blocks.
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