| Vinyl stannanes hold an important place in organic synthesis. They can be used in a variety of roles and their preparation has been the topic of many studies. One means of preparing a vinyl stannane is to hydrostannate an alkyne. This process can be catalyzed by palladium, as first demonstrated by Oshima and coworkers. A high degree of regioselectivity is almost always desired in these transformations, and this warrants the need for a systematic study on what structural features can influence the regiochemical outcome of the reaction. In this study a variety of terminal alkynes were subjected to Pd(O) mediated hydrostannylation conditions with either a hydroxyl, methoxy, or acetate functional group in close proximity. It was shown here that the oxygen functionalities enhance formation of the internal stannane, either by polarization of the carbon-carbon triple bond or via palladacycle intermediacy. Among the functional groups studied R was observed that the acetate functional group had a greater directing effect then either the hydroxy or methoxy group. |
