Preparation and Reactions of Indium Reformatsky Reagents

The highly reactive indium powder reported in Sections 6.1 and 6.2 reacts readily with a-haloesters to give an indium Reformatsky-type reagent which will add to ketones and aldehydes to give p-hydroxy esters. The Reformatsky reaction using zinc metal has been used in the preparation of p-hydroxy esters for many years. Recent improvements have made this reaction a very reliable reaction (see Section 3.10). 

The activated indium powder was prepared by reducing anhydrous InCls (Alfe ultrapure) with freshly cut potassium metal in dry, freshly distilled xylene. The mixture is heated to reflux and stirred with a magnetic stirrer under argon for 4-6 h, yielding a light black powder  

Reaction of this activated indium metal with a-haloesters is rapid. For example, reaction of a mixture of ethyl-a-bromoacetate and cyclohexanone in xylene at 55°C for 2 h gives an almost quantitative yield of the corresponding P-hydroxyester. The activated indium will also react with ethyl-a-chloroace-tate. In this case reaction for 7 h at 55°C in xylene gave a 42% yield of the p-hydroxy ester. In contrast, commercial indium metal (325 mesh) was 

The reaction of the black indium powder with the a-bromoacetate can be readily observed by the rapid disappearance of the black powder and the formation of a brownish-yellow material. The proposed structure for the intermediate indium compounds is (EtOCOCH2)2lnBr. This is based on an analysis of the material which was xylene soluble and showed an In/halide ratio of 1.05 1.00. The overall reaction scheme is shown in Equation 6.1. 

When we extracted the brownish-yellow solid with THE, in which it is much more soluble, we obtained different analysis results. In this case it was found that the K In halide ratio was 0.85 1.00 2.02 and it contained 25.6% of In. This fits the structure of the ate complex of (EtOCOCH2)2lnBr with KCl shown in Equation 6.2. 

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