Characterization and Utilization of the Elusive α,β-Unsaturated N-Tosyliminium: the Synthesis of Highly Functionalizable Skipped Halo Enynes

A formal haloalkynylation of allenamides has been described for the synthesis of highly stereo- and regioselective skipped halo enynes. Exclusive.- regioselectivity is achieved through the intermediacy of a conjugated N-tosyliminium intermediate-direct evidence for the formation of which was validated by NMR and HRMS. Quantum mechanical computations reveal that the reactive intermediate geometry is key to controlling the 1,2- or 1,4-regioselectivity of alkyne interception. Divergent access to elusive unsaturated systems has also been reported.

Automated summary

A formal haloalkynylation of allenamides has been described for the synthesis of highly stereo- and regioselective skipped halo enynes. The study demonstrates exclusive regioselectivity through the intermediary of a conjugated N-tosyliminium intermediate, with evidence validated by NMR and HRMS. Quantum mechanical computations reveal the importance of reactive intermediate geometry in controlling the regioselectivity of alkyne interception, providing divergent access to elusive unsaturated systems.