A new synthesis of indolin-3-one derivatives

Indolin-3-one scaffold occur in the core structure of a large number of compounds with pharmaceutical and biological importance. In particular, 2-spirocyclopentane-indolin-3-ones are reported in literature as components of several alkaloids with interesting biological properties or as intermediates for the synthesis of active pharmaceutical compounds. Moreover, they share with the corresponding 2-methylene-indolin-3-ones emergent applications as functional fluorescent dyes. Taking into account these premises and our experiences in the transition metal catalyzed synthesis and functionalization of indole derivatives, we decided to explore the reactivity of 4H-furo[3,2-b]indoles in the presence of gold(I) activated π-systems for the synthesis of new classes of indolin-3-one derivatives. In particular, employing N-allenamides or propargylic esters, a careful screening of the gold(I) catalysts allowed for the synthesis of two different classes of indolin-3-ones through gold-promoted cascade sequences involving functionalization at the furan moiety followed by a ring-opening event. The obtained results will be presented with particular focus on the optimization of catalytic reaction conditions and on reaction mechanism.