Alkylchrom‐ und Alkylmangan‐Reagenzien, IV. Über die Aldehyd‐ und cheleselektive Alkylierung organischer Carbonylverbindungen mit Monoalkylchrom(III)‐Reagenzien

Abstract

Alkylchromium and Alkylmanganese Reagents, IVril. -On the Aldehyde and Cheleselective Alkylation of Organic Carbonyl Compounds with Monoalkylchromium(II1) ReagentsMonoalkylchromium(II1) reagents, prepared in crystalline P-position are methylated by MeCrC12(thf),, allowing the form or in solution, alkylate aldehydes but normally not ke-highly selective ("cheleselective") methylation of such ketones tones. Ketones with a basic group (HO, MeO, Me,N) in a-or in the presence of normal ketones. Chem.

1,2-Amino Alcohols via Cr/Photoredox Dual-Catalyzed Addition of α-Amino Carbanion Equivalents to Carbonyls

“…To our great surprise, our protocol could also be used for the alkylation of ketones. This is especially noteworthy, as it was previously shown that alkyl-Cr III species do not react with carbonyl electrophiles other than aldehydes, further distinguishing our catalytic system from classical Cr-mediated approaches . Acyclic ( 3ac – 3af ) and cyclic ( 3ag – 3aq ) ketones containing functional groups such as thioethers ( 3aj ), difluoromethylene groups ( 3ak ) or spirocyclic acetals ( 3al ) were all compatible with this reaction.…”

Participation of the α,α‘-Diiminopyridine Ligand System in Reduction of the Metal Center during Alkylation

“…Thus, the formation of the divalent 5 clearly indicates that even a mild alkylating agent may promote the reduction of the metal center. This is especially striking in the case of trivalent Cr when we consider the unusually high stability and chemical inertness of the Cl 2 CrMe moiety capable of resisting the attack of HCl and whose stability should increase even further while in combination with the diiminato ligand. Thus, ligand involvement in the reduction remains a distinct possibility.…”

In Situ Formation of Allyl Ketones via Hiyama−Nozaki Reactions Followed by a Chromium-Mediated Oppenauer Oxidation

“…On the other hand, when ketones 12l and 12m (Scheme ) 24 were used as oxidants instead of benzaldehyde, only very small amounts of oxidation products were detected. Ketones are inefficient as hydrogen acceptors, probably because coordination at the sterically crowded chromium(III) center does not take place easily …”

“…The reaction is reversible, and thus, depending on the conditions, the backward reaction, the Meerwein−Ponndorf−Verley reduction, should also be possible (Scheme a) . Indeed, such a reduction of aldehydes and ketones to alcohols in a similar chromium-mediated reaction, using sec -BuCrCl 2 , was reported . This reduction was explained by assuming a transition state quite similar to that accepted for the Oppenauer−Meerwein−Ponndorf−Verley (OMPV) equilibrium reaction…”