Electrochemical synthesis of allenyl silanes and allenyl boronic esters

Allenyl silanes and boronates are pivotal building blocks in organic synthesis. Nevertheless, their synthesis requires the manipulation of transition metal or highly reactive species. Hence, the development of more sustainable protocol is highly sought after. Here we show the electrochemical synthesis of allenyl silanes and allenyl boronic esters. This catalyst-free method proceeds under mild reaction conditions. The protocol for the synthesis of allenyl silanes shows an excellent efficiency and a good functional group tolerance. The allenyl silanes are isolated in good yields (28 examples, 45-95% yields) without the use of a transition metal catalyst and under mild reaction conditions. A similar protocol is developed for the synthesis of allenyl boronates, which are obtained in low to moderate yields (13 examples, 5-55% yields). Finally, a mechanism based on an oxidative generation of the silyl and boryl radicals is suggested to access these classes of allenes.