Abstract
Herein, we report a mild and highly regioselective Rh(iii)-catalyzed non-oxidative [5 + 1] vinylic C–H annulation of 2-alkenylanilides with allenyl acetates, which has been elusive so far. The reaction proceeds via vinylic C–H activation, regioselective 2,3-migratory insertion, β-oxy elimination followed by nucleophilic cyclization to get direct access to 1,2-dihydroquinoline derivatives. The strategy was also successfully extended to C–H activation of 2-alkenylphenols for constructing chromene derivatives. In the overall [5 + 1] annulation, the allene serves as a one carbon unit. The acetate group on the allene is found to be crucial both for controlling the regio- and chemoselectivity of the reaction and also for facilitating β-oxy elimination. The methodology was scalable and also further extended towards late stage functionalization of various natural products.
Highlights
Controlling regio- and chemoselectivity are the major challenging factors that impede the use of allenes in transition metal catalyzed C–H functionalizations in comparison to other p-systems like alkenes and alkynes.[1]
Development of non-oxidative processes bypassing the toxic metal-oxidants are desirable for achieving sustainable alkenyl C–H annulations. Addressing all these aspects associated with allenes and alkenyl C–H annulation, we demonstrate a robust Rh(III)-catalyzed C–H nonoxidative [5 + 1] annulation of 2-alkenylanilides or 2-alkenylphenols with allenyl acetates to access 1,2-dihydroquinoline or chromene derivatives (Scheme 1c)
As stereo-electronic attributes of allene-substituents play a key role in controlling their reactivity and selectivity of carbometalation, we commenced our initial investigation by studying the reaction of N-tri yl protected 2-alkenylanilide 1a with differently substituted allenes under Rh(III)-catalysis (Scheme 2)
Summary
Controlling regio- and chemoselectivity are the major challenging factors that impede the use of allenes in transition metal catalyzed C–H functionalizations in comparison to other p-systems like alkenes and alkynes.[1]. Addressing all these aspects associated with allenes and alkenyl C–H annulation, we demonstrate a robust Rh(III)-catalyzed C–H nonoxidative [5 + 1] annulation of 2-alkenylanilides or 2-alkenylphenols with allenyl acetates to access 1,2-dihydroquinoline or chromene derivatives (Scheme 1c). As stereo-electronic attributes of allene-substituents play a key role in controlling their reactivity and selectivity of carbometalation, we commenced our initial investigation by studying the reaction of N-tri yl protected 2-alkenylanilide 1a with differently substituted allenes under Rh(III)-catalysis (Scheme 2).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
