Journal
ADVANCED SYNTHESIS & CATALYSIS
Volume 364, Issue 24, Pages 4281-4288Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adsc.202200686
Keywords
palladium; heterocycles; cross-coupling; cyclization
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Funding
- Polish National Science Centre [2016/22/E/ST5/00537]
- Wroclaw Centre for Networking and Supercomputing [518]
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This study describes the Pd-catalyzed tandem cyclization/coupling of internal β-propargylic β-ketoesters with (hetero)aryl bromides. Two protocols are established to selectively produce either 2-benzylidene-dihydrofurans or 2-benzyl-furans. The proposed catalytic cycle involves oxidative addition, substitution of bromide with alkyne, rate-limiting anti-selective 5-exo-dig oxocyclization, deprotonation of the oxonium intermediate, and reductive elimination.
Pd-catalyzed tandem cyclization/coupling of internal beta-propargylic-beta-ketoesters with (hetero)aryl bromides is described. Two protocols are established which selectively lead to 2-benzylidene-dihydrofurans, when isomerization is inhibited under mild conditions (temp. <= 40 degrees C and weak base - K2CO3), or to 2-benzyl-furans when base-induced aromatization is enabled. A catalytic cycle involving oxidative addition, substitution of bromide with alkyne, rate limiting anti-selective 5-exo-dig oxocyclization followed by fast deprotonation of the oxonium intermediate, and reductive elimination is proposed based on detailed experimental and theoretical studies.
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