Experimental and computational studies on rhodium-catalyzed C4(5)_aryl–H activation/annulation of imidazoles with alkynes: facile synthesis of six types of N-heterocycles

Abstract

C–H annulations at N- and C2-aryls of an imidazole have been well researched, while the annulation on C4(5)-aryls especially the reactivity and site-selectivity among these aryls remain unknown. Herein, a...

Hydrazone-oxime Selectively Directed Redox-Neutral [4 + 2] Annulations Cascade with Alkynes and Iodonium Ylides to Build 1,1′-Biisoquinoline Mono-N-oxides

“…When hydrazone-oxime 1a was subjected to Condition A in the presence of CD 3 OD, a selective deuterium incorporation was observed at the hydrazone side (15% D versus 0% D; Scheme a), without deuterium incorporation at the oxime side. In contrast, deuterium incorporation was observed at the oxime side for dioxime 9 (Scheme b) . These two experiments clearly indicate that hydrazone has higher DG-power over oxime, which might be due to the stronger electron-donating ability of NH 2 than OH, resulting in the high selectivity for the first C–H activation.…”

“…Recently, we reported a C–H activation/bidirecting group strategy for the synthesis of 1,1′-biisoquinolines from dioximes and alkynes . Consequently, we became intrigued by probing readily available, nonsymmetric, and electron differential dual-DG as chemoselectivity ensuring entities in unsymmetric double C–H activation to synthesize 1,1′-biisoquinoline N -oxides.…”

Mechanistic insights into an NH4OAc-promoted imine dance in Rh-catalysed multicomponent double C–H annulations through an N-retention/exchange dual channel

“…On the one hand, Rh-catalyzed C–H annulation has been developed as an efficient and frequently-used method to access N-heterocycles; 6 but multicomponent cyclization via Rh catalysis is underdeveloped, 7 especially for four or more component reactions. Recently, Li et al realized a C–H activation/dual-directing group (DDG) strategy for multi-component C–H annulations to construct 1,1′-biisoquinolines (1,1′-BIQs) 8 which cannot be obtained from the known C–H activation/1,3-diyne strategy. 9–12 These linear DDGs may form bidentate ligands to poison the metal catalyst; and other unwanted Z / E isomers may also be generated in their preparation.…”