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Rhodium-catalyzed reactions of (Z)-2-EN-4yne acetates with arylboronic acids
This study is the first example of rhodium(I)-catalyzed arylative SN2Êº type reaction of (Z)-2-en-4-yne acetates with arylboronic acids leading to E-configured vinyl-allenes with an aryl moiety. The coordinative interaction of the rhodium with carbonyl oxygen promoted the -elimination of Rh(I)-OAc from the alkenylrhodium intermediate in both syn- and anti-modes, with the syn-elimination being the major path. DFT calculations revealed that a conformer of this intermediate which can lead to the E-configured vinylallene product via the syn-elimination mode, is energetically the most favorable conformer. The rhodium-catalyzed procedure is not applicable to reactions involving (E)- configured enyne acetates, because the geometry of the alkenylrhodium intermediate that is derived from the corresponding E-enyne acetate would not allow such coordinative interaction to occur.