Reformatsky reactions electrochemical

Bieber reported that the reaction of bromoacetates is greatly enhanced by catalytic amounts of benzoyl peroxide or peracids and gives satisfactory yields with aromatic aldehydes. A radical chain mechanism, initiated by electron abstraction from the organometallic Reformatsky reagent, is proposed (Scheme 8.27).233 However, an alternative process of reacting aldehydes with 2,3-dichloro-l-propene and indium in water followed by ozonolysis provided the Reformatsky product in practical yields.234 An electrochemical Reformatsky reaction in an aqueous medium and in the absence of metal mediator has also been reported.235... 

Electrochemical Reformatsky reaction promoted by sacrificial anodes 803... 

The use of Fe, indium, and zinc as sacrificial anodes in the electrochemically assisted Reformatsky reaction of ethyl 2-bromoalkanoates with succinic anhydride is found to be effective, giving l-ethyl-3-oxohexanedioates in 49 80%... 

The mechanism of the Zn chloride-assisted, palladium-catalyzed reaction of allyl acetate (456) with carbonyl compounds (457) has been proposed [434]. The reaction involves electroreduction of a Pd(II) complex to a Pd(0) complex, oxidative addition of the allyl acetate to the Pd(0) complex, and Zn(II)/Pd(II) transmetallation leading to an allylzinc reagent, which would react with (457) to give homoallyl alcohols (458) and (459) (Scheme 157). Substituted -lactones are electrosynthesized by the Reformatsky reaction of ketones and ethyl a-bromobutyrate, using a sacrificial Zn anode in 35 92% yield [542]. The effect of cathode materials involving Zn, C, Pt, Ni, and so on, has been investigated for the electrochemical allylation of acetone [543]. 

The Reformatsky reaction can also be performed electrochemically either directly or using a mediator. Ni-catalysis has proven to be an efficient way to prepare j3-hydroxy ester or nitrile from the corresponding a-chlorocompounds (Table 14) [94]. Here again the first step is the oxidative addition of the cathodically generated Ni°bpy to the halocompound. The nature of the sacrificial anode also plays a crucial role in this reaction, though the formation of an organozinc intermediate has not been fully demonstrated. 

The authors observed that the applied quantity of electricity (0.2-0.5 F) was always lower than the expected quantity on the basis of Zn consumed (1 g atom). This difference reflects the concurrence of two processes at the anode surface, where the electrochemically promoted reaction (Figure 4) coexists with a classic zinc metal-promoted Reformatsky reaction. Indeed, the electrochemical process produces at the working anode a perfectly clean zinc metal surface, very reactive towards the a-bromoester. 

In the second study, the electrochemically promoted Reformatsky reaction is carried out by electrolysing a DMF solution of Bu4NBr, ZnBr2 (catalytic), Ni(bipy)3(BF4)2 (catalytic),... 

Nickel catalysis in the electrosynthesis of aryl- and heteroarylzinc reagents, and in the electrochemical Reformatsky and allylation reactions using alkyl chlorides... 

Finally, the use of ultrasound to entrain Reformatsky reactions deserves mentioning.37 Since a conventional laboratory cleaning bath is usually sufficiently effective, this easily adaptable method should find wider use in particular for large scale preparations. The same may hold true for the use of sacrificial anodes and/or for Reformatsky-type reactions triggered by electrochemical means.38... 

In an electrochemical version of the modified Reformatsky reaction a sacrificial indium anode is used. Using this method, fully substituted /3-lactones are obtained directly from the proper substrates. 

A one-pot preparation of 4-iodomethyloxetan-2-one is reported (93SL899). Electrochemically generated organometallic compounds react with ketones in a Reformatsky reaction to give esters or lactones (93AG1218) and the formation of P-lactones is favoured when a sacrificial indium anode is used (94JOC3161). 

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