Selective, Radical-Mediated Additions of Thiols to Alkenes in the Presence of Protected Alkynes

The addition of thiols to alkenes (thiol-ene reactions) and thiols to alkynes (thiol-yne reactions) is rapidly expanding field since it shows great promise as a powerful pathway for polymer and macromolecular synthesis. The current limitation for these reactions is the ability to carry out selective thiol-ene and thiol-yne additions. Thiol additions in competitive ternary systems result in complex mixtures of products. Previous studies have shown that sequential selective addition of a thiol to electron poor Michael acceptors is possible. Through the use of triisopropyl silyl protecting groups bound to terminal alkynes, it is possible to sterically disfavor the addition of thiols to alkynes while still allowing thiol-ene additions. This protocol will allow for the addition of two different thiols though a two step radical pathway. The two step radical addition allows for broader molecular tailoring of complex systems and synthetic flexibility in the choice of different substrates.