Abstract
Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process.
Highlights
Chemists have long relied on reactions that allow for generation of unstable and reactive intermediates but forcing conditions, as well as strong and unselective reagents are o en required to achieve the desired transformations
Given the central role of enolates in organic synthesis, reactions that allow for modular generation of enolates, e.g., by carbon–carbon bond-forming reactions under neutral conditions and in the absence of strong bases are highly sought a er but have remained elusive
A-Branched carbonyl compounds, in particular carboxylates, are among the most synthetically valuable and medicinally important structural motifs, whose applications range from non-steroidal anti-in ammatory drugs (NSAIDs)13 to versatile reagents for late stage functionalization enabled by resurgent decarboxylative methodologies
Summary
Chemists have long relied on reactions that allow for generation of unstable and reactive intermediates but forcing conditions, as well as strong and unselective reagents are o en required to achieve the desired transformations. Scheme 1 Boron enolates and the deoxygenative a-alkylation/arylation of 1,2-dicarbonyls. We found that the reaction of ester 6 with triethylborane and trimethyl phosphite proceeded cleanly at 50 C in THF, affording a-branched carboxylate 7 in good yield (Scheme 2).
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