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Synthesis of 2,3-Substituted Thienylboronic Acids and Esters

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journal contribution
posted on 28.11.2003, 00:00 by Claus Christophersen, Mikael Begtrup, Søren Ebdrup, Henning Petersen, Per Vedsø
A noncryogenic protocol for the synthesis of 2-substituted 3-thienylboronic acids and esters as well as 3-substituted 2-thienylboronic acids and esters has been developed. Electrophiles were introduced regiospecifically in the 2-position of 2,3-dibromothiophene and in the 3-position of 2-bromo-3-iodothiophene by halogen−magnesium exchange followed by quenching with electrophiles. Palladium-catalyzed borylation of the 2,3-substituted halothiophenes with pinacolborane and P(t-Bu)3 as ligand for Pd produced 9 and 10. The borylation protocol was tolerated by a range of functional groups; however, strongly electron-withdrawing substituents decreased the stability of the thienylboronic acids and esters.