Reactions of PhCOPdX(PPh 3) 2 (X  I, Cl) with alkylmetals under carbon monoxide; formation of α-diketones and α-hydroxyketones under stoichiometric and catalytic conditions

Abstract

The reactions of PhCOPdX(PPh 3) 2 (Ia: X  I; Ib: X  Cl) with alkylmetals under carbon monoxide have been investigated. The reactivity of ethylmetals toward Ia was found to decrease in the order: Et 2M (M  Zn, Cd, Hg) ∼ etZnCl ∼ EtCu > EtMgBr ∼ EtMnI ∼ Et 3Al > Et 2AlCl > Et 3B ∼ Et 4Sn (no reaction). In these reactions, the simple coupling product, PhCOEt (II) and/or the carbonylative coupling products IIIa–IIIc (IIIa: PhCOCOEt; IIIb: PhCEt(OH)COEt; IIIc: PhCOCEt 2 (OH)) were formed depending on the nature of the ethylmetal. Et 2Hg and Et 3Al gave exclusively II. EtMgBr, EtCu, and EtZnCl gave both of II and III. EtMnI and Et 2M (M  Zn, Cd) selectively gave III. The use of Ar 2Zn(Ar  Ph, p-Tol) in place of Et 2Zn gave decreased yields of the carbonylative coupling products. The palladium complex Ib showed almost the same reactivity toward Et 2Zn as Ia. Further to this palladium-catalyzed carbonylation reactions of PhCOCl with alkylmetals were examined. The reaction with Et 2Zn catalyzed by PdCl 2(PR 3) 2 (R  Ph, pFC 6H 4) afforded III (mainly IIIb and IIIc, about 200%/Pd). The combination of Pd(PPh 3) 4 and Et 3Al more effectively afforded III (mainly acyloin-type reduced products, about 900%/Pd).