Mild and Practical Indole C2 Allylation by Allylboration of in situ Generated 3‐Chloroindolenines

C2 allylation of indole derivatives is a challenging but important transformation given the biological relevance of the products. Herein we report a selective C2 allylation strategy that proceeds via allylboration of in situ‐generated 3‐chloroindolenines. The reaction is mild, practical, and compatible with a wide range of C3‐substituted indoles. As allylboronates are readily accessible from commercial precursors, various substituted allyl moieties can be introduced using the same protocol. To showcase the utility of this method we applied it to the synthesis of the natural product, tryprostatin B. ALL(yl) IN(dole)!: Allylboration of in situ generated 3‐chloroindolenines allows the mild and operationally simple C2 allylation of 3‐substituted indoles. The reaction has a broad functional group tolerance and is compatible with various substituted allylboronates. The utility of this method is demonstrated by the total synthesis of tryprostatin B.