New Preparation of Benzylic Aluminum and Zinc Organometallics by Direct Insertion of Aluminum Powder

Abstract

The reaction of commercial Al-powder (3 equiv) and InCl(3) (1-5 mol %) with benzylic chlorides provides various functionalized benzylic aluminum sesquichlorides under mild conditions (THF, 20 °C, 3-24 h) without homocoupling (<5%). These new benzylic organometallics reacted smoothly with various electrophiles (Pd-catalyzed cross-couplings, or Cu-mediated acylations, allylations, or 1,4-addition reactions). Electron-poor benzylic chlorides or substrates prone to Wurtz coupling can be converted to benzylic zinc compounds by the reaction of Al-powder in the presence of ZnCl(2).

Direkte Pd‐katalysierte Kreuzkupplung von funktionalisierten Organoaluminiumreagentien

“…Benzylaluminiumsesquichloride des Typs 6 (1.25 Äquiv. ), hergestellt durch Al‐Insertion (in Gegenwart von 3 Mol‐% InCl 3 ) in die entsprechenden Benzylchloride 5 ,14d, 25 gehen ebenfalls die Kreuzkupplung mit zahlreichen Aryl‐ und Heteroaryliodiden und ‐bromiden ein, wobei die erwarteten Produkte 7 a – e erhalten werden (Schema ) 26. Oct‐Al 2/3 X, das durch Al‐Insertion (3.0 Äquiv.…”

Copper-catalyzed arylation of alkyl halides with arylaluminum reagents

“…In addition, Al also has low toxicity and is an inexpensive and earth-abundant metal. Organoaluminum reagents can be prepared directly from metallic aluminum [ 13 – 15 ], which further highlights the potential scope of these reagents in organic synthesis. However, despite extensive investigations and applications of organometallic reagents of Si, B, Mg, Zn and Sn in cross-coupling, the utility of organometallic complexes of Al are limited [ 13 – 14 16 – 21 ].…”

Organoaluminum‐Mediated Direct Cross‐Coupling Reactions

“…[3] Organoaluminum reagents occupy ac entral position in synthetic organic and organometallic chemistry because of their low cost, ready availability,low toxicity,and exceptional Lewis acidity. [2,6] However,i nr ecent years,n ew coupling procedures that do not require those additives have also been developed:for example,1)byappropriately tuning the coordination of aluminum (by using heteroleptic ligands, [7] triarylaluminum compounds such as Ar 3 Al, [8,9] or am ore reactive organoaluminate complex [10] ), 2) by using another transition-metal catalyst such as Ni [11] or Fe, [9,12] and 3) notably,byusing aryl-or benzylaluminum reagents freshly prepared in situ with proper Pd catalysts and ligands. [5] Thei nitial methods for cross-coupling with organoaluminum usually required ac o-catalyst such as zinc or indium salts to accelerate the reaction.…”