Ethers propargylic, reaction with Grignard reagents

Trisubstituted allenes. The reaction of aliphatic Grignard reagents with a 1,1-disubstituted propargylic acetate (1) in ether results in formation of a tri-alkylallene (2). Yields are satisfactory with Grignard reagents of primary halides, but less satisfactory when R - is an aryl group. ... 

The reaction of propargylic ethers proceeds through an addition-elimination pathway, which docs not involve the coppcr(III) intermediate. The stereochemical outcome varies with the nature of the halogen component of the Grignard reagent of RMgX6Sc. If the halogen is chloride, overall syn selectivity is obtained however, anti substitution results in the case of iodide. 

THF if CuBr is present.1393 The reaction takes place either with or without allylic rearrangement.1394 Propargylic ethers give allenes.1395 Vinylic ethers can also be cleaved by Grignard reagents in the presence of a catalyst, in this case, a nickel complex.1396 Silyl enol ethers R2G=CROSiMe3 behave similarly.1397... 

THF is useful in the malonic ester synthesis since it dissolves many sodio derivatives. Use of aqueous THF facilitates diazotization of salts of aminopolyphenyls which are sparingly soluble in water and is recommended also for the Schiemann reaction. It is superior to ether as solvent for coupling of an acetylenic Grignard reagent with a propargylic halide. Cremlyn and Chisholm found THF superior to dioxane or Cellosolve as solvent for the hydrogenation of cholesterol at ordinary temperature and pressure with perchloric acid as catalyst. 

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