| Popis: |
2-Aminobiaryls are privileged scaffolds and their cogent synthesis and diversifications, particularly through the C-H bond activation strategy, is a continuous enterprise in organic synthesis. In this realm, capitalization on susceptible native amine (-NH2) directing group is beneficial but increasingly challenging owing to its innate nucleophilic reactivity. Also, the C-H activation reactions of this class of substrates have traditionally been restricted to the cross-ring C-H bond as the ortho C-H functionalization presumably requires the formation of a strained high-energy four-membered metallacycle. Herein, we report the first example of free amine-directed ortho C-H activation reaction of 2-aminobiaryls under high-valent Cp*Co(III)-catalysis, enabling regio- and stereoselective allylation reaction in high yields. The protocol engages vinyl cyclopropanes as allyl synthons where the C-C bond construction event was tunneled to a C-C activation process to forge internal olefin with exclusive (E)-selectivity. The products were judicially used to access high-value benzo[d]isoxazoles and dihydro phenanthridine derivatives. Mechanistic experiments and DFT calculations have also been conducted to unravel the rationale behind the unique site selectivity, where the thermodynamic constraints of the corresponding intermediates favoring the ortho C-H activation over cross-ring functionalization. |
