Cu-catalyzed silylation of alkynes: a traceless 2-pyridylsulfonyl controller allows access to either regioisomer on demand.

The Cu-catalyzed silylation of terminal and internal alkynes bearing a 2-pyridyl sulfonyl group (SO2Py) at the propargylic position affords a breadth of vinyl silanes in good yields and with excellent regio- and stereocontrol under mild conditions. The directing SO2Py group is essential in terms of reaction efficiency and chemoselectivity. Importantly, this group also provides the ability to reverse the regiochemical outcome of the reaction, opening the access to either regioisomer without modification of the starting substrate by virtue of an in situ base-promoted alkyne to allene equilibration which takes place prior to the silylcupration process. Furthermore, removal of the directing SO2Py allows for further elaboration of the silylation products. In particular, a one-pot tandem alkyne silylation/allylic substitution sequence, in which both steps are catalyzed by the same Cu species, opens up a new approach for the access to either formal hydrosilylation regioisomer of unsymmetrical aliphatic-substituted internal alkynes from propargyl sulfones.