Synthesis of 2,3-substituted thienylboronic acids and esters.
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.
Christophersen
Claus
C
Novo Nordisk A/S, Novo Allé, DK-2880 Bagsvaerd, Denmark. clcp@novonordisk.com
Begtrup
Mikael
M
Ebdrup
Søren
S
Petersen
Henning
H
Vedsø
Per
P