Electrophilic activation of allenenes and allenynes: analogies and differences between Brønsted and Lewis acid activation.

This Tutorial Review summarizes recent examples of electrophilic activation of allenes with particular focus on analogies and differences between Lewis and Brønsted acid activation of these versatile substrates. The aim of this article is to present a general overview of the possibilities offered to chemists using complementary modes of catalysis and to emphasize advantages and limitations of each approach, thereby providing a means to expand the scope of this powerful synthetic methodology.