Halogen-Magnesium Exchange Reactions

Although the mechanism of halogen-metal exchange reactions is not clear, three mechanisms are supposed - reaction via four-centered transition states, via radical intermediates, and via halogen ate complexes. 

The effect of solvents on the exchange reactions has been studied [67]. The extent of exchange is proportional to the solvating power of the solvent and increases in fhe order diethyl ether diefhoxyethane methoxyethoxyethane di-glym tetrahydrofuran dimethoxyefhane. 

Oxidation of alkenes with a peracid is an exothermic reaction and, to 

2 REACTIONS IN WHICH A REACTIVE INTERMEDIATE EASILY DECOMPOSES IN MACROBATCH REACTORS 

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Halogen-magnesium exchange reactions with triorganomagnesates were reported independently from academia" and industry in 2001. 

Preparation of some azulenylmagnesium species was achieved by the halogen-magnesium exchange reactions of iodoazulenes with lithium tributylmagnesate at low temperatures (equations 29-33) . The reactions offer access to a variety of functionalized azulenes including azulenylphosphine, -stannane and -boronic ester. 

A. Generation of Magnesium Carbenoids by Halogen-Magnesium Exchange Reaction... 

An intramolecular 1,5-C,H insertion reaction was reported from substituted bromo-iodoalkane and halogen-magnesium exchange reaction (equation 24) °. Indeed, treatment of bromoiodoalkane (86) with i-PrMgCl in ether at —78°C to —20°C resulted in the formation of magnesium carbenoid 87. The 1,5-C,H insertion of 87 took place to afford a cyclopentane derivative (88) however, the yield was not satisfactory. 

Oshima, K. Selective halogen—magnesium exchange reaction via organomagnesium ate 483 complexes./. Org. Chem. 2001, 66, 4333—4339. 

The halogen-magnesium exchange reaction can be easily applied to solid-phase synthesis, affording polymer-bound Grignard reagent, otherwise unavailable (Scheme 27). 

Recent topics related to halogen-magnesium exchange reactions and organomag-nesium-mediated radical reachons will be discussed in subsequent sections. 

Practical Examples of Halogen-Magnesium Exchange Reactions... 

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