Formation of Enolates by Halogen-Magnesium Exchange

The exchange reactions of a-iodo ketones and a,a-dibromo ketones have been re- 

6 Miscellaneous Reactions Exchange Reaction of Alkynyl Halides [114] 

In contrast, normal aryl bromides are much less reactive than aryl iodides. Some examples are shown in Tab. 3.8 [117]. 

Entiy Substrate equiv of PrMgCl Time (hj Product Yield (%) 

As is apparent from Tab. 3.8, an ortho methoxy group acts as a metal-directing group. Thus selective exchange occurs at the ortho position of a methoxy group. More than two bromines are necessary to complete the reaction. 

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