Anionic 5- <i>endo-dig</i> cyclizations: an experimental investigation of in-plane aromaticity involving a non-enolate carbanion nucleophile

Cyclitive additions of aliphatic carbanions to non-electrophilic carbon-carbon triple bonds under mild, transition-metal-free conditions are described for the first time. These results confirm theoretical models that invoke in-plane aromaticity to predict the favorability of 5-<i>endo-dig</i> reactions in these systems. In contrast to related Conia-ene cyclizations (5-enolexo-<i>endo-dig</i>), our results generally led to cyclic and allene products in near parity ratios across a broad range of substrates, suggesting that cyclization may proceed <i>via</i> an early ambimodal transition state. Experimental results are presented with a view to refining existing mechanistic models for this growing class of alkyne reactions.