Strictly “Pair”-Selective and Economical Synthesis of Conjugated Diynes via Pd-Catalyzed Reaction of Terminal Alkynes with 1,1-Dichloroethylene, Elimination with LDA, and Subsequent Transformations

Various unsymmetrically substituted conjugated diynes can be synthesized in a completely “pair”-selective manner via Pd-catalyzed reaction of terminal alkynes with 1,1-dichloroethylene in the presence of Pd(PPh 3 ) 4 followed by elimination with 2 equiv of lithium diisopropylamide (LDA), zincation with ZnBr 2 or ZnCl 2, and Pd-catalyzed cross-coupling with aryl and alkenyl iodides and bromides. The desired unsymmetrically substituted conjugated diynes have been obtained in >80% yields except in two cases where an alkenylzinc reagent generated in situ from ( E )-3-iodo-2-propenol was used. The use of 1,1-dichloroethylene renders this method more economical than those involving 1,2-dihaloethylenes previously reported.