The free-radical hydrostannylation of alkynes to create vinylstannanes is a central transformation in the general family of addition reactions and it has been widely employed in synthetic chemistry in academic and industrial laboratories since its discovery in the 1960s. This valuable transformation has been extensively studied and while every published mechanism involves solely radical intermediates, this appears not to be correct. In this study we have discovered that trace molecular oxygen is necessary for any hydrostannylation to occur with a wide selection of alkynes leading us to propose a hybrid single-electron transfer (SET)/radical propagation mechanism. This newly proposed mechanism, which is expected to proceed through cationic intermediates, has been evaluated experimentally and theoretically and accurately predicts the regio- and stereoselectivity of this addition in the presence of O2, something that current mechanisms cannot. This critical new knowledge will serve as a valuable tool for synthetic chemists to prepare increasingly complex and prized vinylstannanes for a wide variety of applications.

AIBN-mediated alkyne hydrostannylation: It's not as radical as you think!

246th National Meeting (2013)

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