Preparation and Coupling Reactions of Thienylmanganese Halides

Typical Preparation of Functionalized Benzylic Manganese Halides and Their Cross-Coupling Reactions with Aryl Iodides under a Palladium Catalyst 

Acylation-reduction, lithiation-alkylation, thiophene ring construction, and Grignard cross-coupling with bromothiophene are the representative methods for the preparation of alkyl- and arylthiophenes [46]. 

We reported a facile synthesis of 3-bromo-4-thienylmanganese bromide and 4-substituted 3-thienylmanganese bromides via the direct oxidative addition 

As shown in Table 8.18, 3-bromo-4-thienylmanganese bromide was formed as a major product from the reaction of 1 equiv of 3,4-dibromothiophene and 2equiv of Mn [47]. This reagent easily underwent a cross-coupling reaction with acid chlorides and aryl iodides. According to the high-resolution mass spectra of the products of entries 1,4,5, and 6 in Table 8.18, the second bromine atom of the thiophene ring is still retained. 

The same strategy was applied to 4-substituted 3-bromothiophenes to make unsymmetrical 3,4-disubstituted thiophenes. As shown in Table 8.19, crosscoupling products were obtained in moderate yields (36-66%) under mild conditions. Oxidative additions of Mn to the 4-substituted bromothiophenes were performed at rt in 5 h, and the successive coupling reactions of thienylmanganese bromides with benzoyl chlorides afforded unsymmetrical 3,4-disubstituted thiophenes at rt in 30 min without a catalyst (Table 8.19, entries 1 and 2). 

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