Methylene bromide, coupling reagent

Methylene bromide can function as the coupling reagent if it is used in an excess. This unusual coupling reaction succeeds, presumably, because the intermediate a-bromo ether, 3, reacts much more rapidly with the phenoxide endgroup of another polymer than methylene bromide does to produce the formal linked product, 4. 

Methylene chloride also acts as a coupling reagent but is less effective than methylene bromide. Examples of coupling material containing structure are shown in Table II. 

Chloroiodomethane has been used instead of methylene iodide to methylenate cyclic enamines (43). Methylene bromide was applicable to the Simmons-Smith reaction instead of methylene iodide when highly active zinc-copper couple was used 298,558). The resulting BrCH2ZnBr is an effective methylene transfer reagent. 

Stirring zinc dust with AcCl and CuCl (Et20, rt A) produces an active zinc couple capable of reacting with methylene bromide to form the Simmons-Smith reagent Friedrich, E. C. Lewis, E. J. J. Org. Chem. 1990,55, 2491. 

Homoallyl bromide 314, prepared from readily available non-racemic ester 313, was converted to the Grignard reagent, which reacted with non-racemic epoxide, derived from D-maUc acid, to afford the alcohol 305. Ozonolysis of the alkene gave a ketone, which was converted into enol tri-flate 316. Ni-catalyzed cross coupling with trimethylsilylmethyl magnesium chloride afforded the allyl silane, which was converted into the allyl stan-nane 317. The asymmetric allylation of 313 with 317 provided 304 with a ration of 8.5 1. Methyl etherification and oxidative cleavage of exo-methylene... 

The final con und, 33, was prepared by a Grignard cross coupling reaction between diketene (39) and -butylmagnesium bromide in the presence of anhydrous cobalt iodide (30, 34). It is noteworthy that the Grignard reagent attacks the methylene carbon instead of the carbonyl carbon in the presence of cobalt iodide. 

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