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We have disclosed a general and efficient synthetic strategy for polysubstituted pyridines and isoquinolines with high chemo- and regioselectivity. In this methodology, 1-alkynyl imines act as the key compound to undergo a sequential alkynyl imine-allenyl imine isomerization/aza-Diels-Alder reaction/aromatization. In the first place, 1-alkynyl imines were formed in situ by a highly selective multicomponent reaction of isocyanides, arynes, and terminal alkynes and reacted with another molecule of arynes or terminal alkynes to furnish target heterocyclic products in a highly efficient and atom-economic manner. On the other hand, we attempted to prepare 1-alkynyl imines by other approaches to undergo a similar reaction sequence to afford polysubstituted pyridines and isoquinolines with a wider range. Different from the first approach, the second approach utilized the preprepared 1-alkynyl imines to introduce the related different substitutents into the final products: arynes or terminal alkynes bearing substituents different from those of 1-alkynyl imines have been successfully applied for the synthesis a wide variety of pyridines and isoquinolines with diversity.

Many components make light work: A novel synthetic strategy for the preparation of pyridines and isoquinolines in high chemo- and regioselectivity has been developed. By manipulating the reaction conditions, either product can be generated smoothly in a highly efficient and atom-economic manner (see scheme).

The first palladium-catalyzed highly regioselective [3 + 2] cycloaddition reactions of alkylidenecyclopropa[b]naphthalenes 1 with alkenes or alkynes is presented, providing an efficient method for the synthesis of 1(3)-alkylidene-2,3-dihydro-1H-benzo[f]indenes or 1-alkylidene-1H-benzo[f]indenes under mild conditions.