Thiophene-derived diphosphine ligands

In contrast, synthesis of 3,4-diphosphorylthiophenes requires more elaboration because of low reactivity of 3,4-positions of thiophene and unavailability of 3,4-dihalo or dimetallated thiophenes. Minami et al. synthesized 3,4-diphosphoryl thiophenes 16 as shown in Scheme 24 [46], Bis(phosphoryl)butadiene 17 was synthesized from 2-butyne-l,4-diol. Double addition of sodium sulfide to 17 gave tetrahydrothiophene 18. Oxidation of 18 to the corresponding sulfoxide 19 followed by dehydration gave dihydrothiophene 20. Final oxidation of 20 afforded 3,4-diphosphorylthiophene 16. 3,4-Diphosphorylthiophene derivative 21 was also synthesized by Pd catalyzed phosphorylation of 2,5-disubstituted-3,4-dihalothiophene and converted to diphosphine ligand for Rh catalysts for asymmetric hydrogenation (Scheme 25) [47],... 

While BDSfAP (5) has been one of the most successful ligands employed in the intermolecular asymmetric Mizoroki-Heck reaction, many other diphosphine ligands have also been synthesized and tested. Sannicolo and coworkers [20] synthesized novel thiophene-derived axially chiral diphosphine ligands 24 and 25 and applied these to the intermolecular Mizoroki-Heck reactiou of 2,3-dihydrofuran (1) (Scheme 11.13). 

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