Asymmetric [4+2]‐Cycloaddition of Anthracene Derivatives via Hydrazone Activation

Abstract

Enantio‐ and diastereoselective dearomative [4+2]‐cycloaddition reaction between N,N‐dimethylhydrazone derived from 9‐anthracenecarbaldehyde and α,β‐unsaturated aldehydes is reported. The developed strategy utilizes HOMO‐rising activation of diene (via hydrazone formation) and aminocatalytic LUMO‐lowering activation of dienophile (via iminium ion formation). High chemical and stereochemical efficiency have been obtained owing to the application of Jørgensen catalyst. Target cycloadducts were subjected to selected transformations aiming at unmasking the hydrazone moiety that proceeded with preservation of optical purity introduced in the organocatalytic step.

Catalytic asymmetric [4 + 2] dearomative photocycloadditions of anthracene and its derivatives with alkenylazaarenes

“…In order to break the inherent aromatic stability of anthracene, activated functional groups are typically required to assemble on the anthracene ring (Fig. 1C ) 64 . For simple anthracene derivatives and diverse reaction partners with similar poor reactivity to be viable and for conversion to occur under mild reaction conditions, the exploitation of photocatalytic systems to input additional chemical energy from photons has been investigated by chemists 65 .…”

Hydrazone Activation in the Aminocatalytic Cascade Reaction for the Synthesis of Tetrahydroindolizines

“…Recently, we demonstrated that hydrazone activation of (hetero)­aromatic aldehydes constitutes a useful tool for the development of new organocatalytic transformations. − It was shown that such a strategy can be efficiently employed in the asymmetric Friedel–Crafts reaction, (3 + 2)-cycloaddition (for the synthesis of 2,3-dihydro-1 H -pyrrolyzines), or asymmetric [4 + 2]-cycloaddition with hydrazone derived from 9-carboxyanthracene, leading to the formation of the biologically relevant dihydro-9,10-ethaneanthracene scaffold …”

“… 14 − 16 It was shown that such a strategy can be efficiently employed in the asymmetric Friedel–Crafts reaction, (3 + 2)-cycloaddition (for the synthesis of 2,3-dihydro-1 H -pyrrolyzines), 15 or asymmetric [4 + 2]-cycloaddition with hydrazone derived from 9-carboxyanthracene, leading to the formation of the biologically relevant dihydro-9,10-ethaneanthracene scaffold. 16 …”