Development of catalytic reactions triggered by addition of arylrhodium(I) species across alkynes

There has been a considerable progress in the development of the rhodium (I)-catalyzed carbon-carbon bond forming reactions using organoboronic acids during the past decade. In most cases, the intermediate organorhodium(D complexes are hydrolyzed without being used for a further reaction despite their potential usefulness for carbon-carbon bond formation. We then envisaged that the intramolecular trapping of the intermediate species might be feasible if an accepting functional group was placed at an appropriate position in the molecule. In this article, we describe various types of cascade reactions triggered by addition of arylrhodium(D species across alkynes. The resulting alkenylrhodium(I) intermediate subsequently undergoes either (type-i) intramolecular addition across a carbon-heteroatom multiple bond, (type-ii) intramolecular addition across a carbon-carbon multiple bond, or (type-iii) β-oxygen elimination. It is also illustrated that the reactivity order of organorhodium(I) intermediates toward nitriles and esters is opposite to that of organolithium and organomagnesium reagents. The synthetic potential of the rhodium-catalyzed reaction of alkynyl oxiranes with arylboronic acids was demonstrated by applying to the total synthesis of (±)-Boivinianin B.