Thiophene synthesis via 1,1-carboboration

Abstract

Reaction of bis(tert-butylethynyl)sulfide with the boron Lewis acid reagents X-B(C6F5)2 (X = CH3, Cl, C6F5) in pentane at r.t. gave the respective borylated thiophenes in a sequence of 1,1-carboboration reactions. In contrast, bis(phenylethynyl)sulfide reacted with B(C6F5)3 only in a 2 : 1 molar ratio to give a benzothiophene derivative.

A 1,1‐Carboboration Route to Bora‐Nazarov Systems

“…This has resulted in protocols using −H as the migrating group and even alkyl or aryl groups . These advanced 1,1‐carboboration sequences have been used in tandem reactions containing various geminal bis(alkynyl) compounds to give phospholes, thiophenes, and even boroles . Since boryl groups seemed to be suitable migrating groups in 1,1‐carboboration reactions, we tried to extend and apply this method for the synthesis of dihydroboroles via bora‐Nazarov containing reaction sequences.…”

BCl3‐Induced Annulative Oxo‐ and Thioboration for the Formation of C3‐Borylated Benzofurans and Benzothiophenes

“…Whilst B(C 6 F 5 ) 3 was crucial in developing metal‐free alkyne borylative cyclization it leads to zwitterionic products such as A (Scheme ). The use of these species in subsequent functional group transformations is not established, currently limiting their synthetic utility . Using alternative boron Lewis acids such as BCl 3 to effect borylative cyclization enables the formation of organo‐boronic acid derivatives on work‐up, and consequentially access to the myriad of already proven transformations.…”

Advanced 1,1-carboboration reactions with pentafluorophenylboranes

“…29 This effect was used to develop a sequential 1,1-carboboration route to a boryl substituted thiophene derivative. The product 30 was deborylated by treatment with acetic acid.…”

“…We have shown that thiolate substituents can serve as suitable migrating groups in 1,1-carboboration reactions (see Scheme 9 for typical examples). 29 This effect was used to develop a sequential 1,1-carboboration route to a boryl substituted thiophene derivative. The product 30 was deborylated by treatment with acetic acid.…”