Memory of Chirality in Electron Transfer Mediated Benzylic Umpolung Reactions of Arene-Cr(CO)3 Complexes

Abstract

As density functional calculations suggest, Cr(CO) -complexed benzylic radicals (such as 2) exhibit a significant degree of configurational stablility. This was exploited in an efficient method for the electron transfer mediated transformations of readily available 1-arylalkanol-Cr(CO) derivatives 1 to afford alkylated products 3 in good yields and with a high degree of stereochemical retention.

An Enantioselective Approachto Cytotoxic Norcalamenenes via Electron-Transfer-Driven BenzylicUmpolung of an Arene Tricarbonyl Chromium Complex

“…the benzylic umpolung of arene-Cr(CO) 3 complexes. 7 As a precursor for the synthesis of 1 and 2 we considered the chromium complex 3 as a suitable candidate, which would allow aromatic methylation in the position ortho to the methoxy group. The diastereoselective introduction of the isopropenyl side chain could then be imagined by benzylic alkylation of the planar chiral anionic complex 4 from the less hindered face of the ligand.…”

Diastereo‐ und enantioselektive Synthese von Pyrrolo[1,4]benzodiazepinen durch decarboxylierende Photocyclisierung

“…Entscheidend für das Ausmaß an Chiralitätserinnerung ist die Lebensdauer der durchlaufenen Zwischenstufen und deren konformative Flexibilität. Neben Reaktionen mit Carbanionen,1 Monoradikalen2 oder Carbeniumionen3 bieten sich dafür solche von Diradikalen an, da (wenn überhaupt) nur geringe Aktivierungsbarrieren zu überwinden sind. Über diese Variante ist von Giese und Mitarbeitern kürzlich bei der Cyclisierung photochemisch erzeugter Singulett‐1,5‐Diradikale berichtet worden 4.…”

Memory of chirality in reactions involving monoradicals

“…Schmalz, de Koning and coworkers have generated a Cr(CO) 3 -complexed benzylic radical 29r from the corresponding chiral benzylic ether 29 using lithium di-tert-butyl-biphenylide (LiDBB) [45]. This radical is better described as the 17 valence electron resonance structure 29r 0 and it exhibits a significant configurational stability based on a calculated rotational…”