Electronic Character of α,3-Dehydrotoluene Intermediates Generated from Isolable Allenyne-Containing Substrates.

We report here the generation of α,3-dehydrotoluenes, a relatively rare subset of reactive intermediates of the dehydroaromatic family, from isolable allenynes. The substructure motif in the allenyne substrates is distinct from, and complementary to, those found in Myers-Saito/Schmittel-type cycloisomerizations. The reactions reported here give rise to product profiles that provide insight about the electronic nature (i.e., diradical vs. zwitterion vs. cyclic allene) of the particular isomeric DHT(s) that is(are) produced under different reaction conditions differing most significantly in the polarity of the reaction solvent. One example also revealed previously unobserved carbene-like reactivity of the DHT.