Ring‐Closing Metathesis Approach to Heteroaromatic Cations: Synthesis of Benzo[a]quinolizinium Salts

Abstract

Keywords: Synthetic methods / Nitrogen heterocycles / Metathesis / Benzo[a]quinolizinium saltsBenzo[a]quinolizinium salts have been synthesized through ring-closing metathesis reactions of 1-butenyl-2-vinylisoquinolinium, 2-butenyl-1-vinylisoquinolinium and 2-styryl-1-vinylpyridinium salts in the presence of Grubbs and

Operation of the Boomerang Mechanism in Olefin Metathesis Reactions Promoted by the Second-Generation Hoveyda Catalyst

“…This trend is widespread where high concentrations are employed. − High olefin concentrations favor the associative pathways now known , to be accessible for HII , but precluded for GII (which is constrained to react via the rate-determining dissociation of phosphine, and hence four-coordinate Ru-1 ) . Even at high dilutions, however, HII may exhibit superior performance. ,− Of note, reports from pharma indicate that catalysts of the Hoveyda class out-perform GII in several demanding ring-closing metathesis (RCM) reactions . Understanding the mechanistic basis of these performance differences takes on added importance as molecular metathesis catalysts enter a new phase of deployment in process chemistry…”

Recent Advances in the Synthesis of Azonia Aromatic Heterocycles

“…Benzo­[ a ]­quinolizinium was synthesized by classical cyclization methods involving the formation of C4–N5, C6–C7, and C1a–C11a bonds from pyridine and isoquinoline as starting heterocycles. Our approaches based on a key RCM reaction involved C1–C2, C3–C4, and C6–C7 bond formation . The first two strategies are similar to those employed to build the quinolizinum system, whereas the third can only be applied to this system or other polycyclic aromatic heterocycles with similar ring fusion .…”

An Efficient Rh/O2 Catalytic System for Oxidative C–H Activation/Annulation: Evidence for Rh(I) to Rh(III) Oxidation by Molecular Oxygen

“…Isoquinolinium salts are one of the most valuable backbones in natural alkaloids and are widely utilized as dyes, paints, and insecticides as well as pharmaceuticals . Although a number of methods for the synthesis of such compounds are available, many are limited by the lack of generality, narrow functional group tolerance, and lengthy synthetic steps . In 2008, Jones developed a novel reaction leading to these compounds using 2-phenylpyridine, N -benzylidenemethylamine, and dimethyl acetylenedicarboxylate (DMAD); the reaction proceeds via Rh-mediated C–H activation and requires a stoichiometric amount of [{Cp*RhCl 2 } 2 ] .…”