Oxygen as the Substituent

These allenes are very important for organic synthesis and their use is discussed in Chapter 8. For their synthesis usually a strong base is needed, typically KOtBu. There are many examples most of them cover the isomerization of a propargylic ether to the corresponding allenyl ether. 

The significance of this reaction is reflected by the isomerization of the smallest representative, propargyl methyl ether, with a number of references from 1968 up to 2000(167-175]. 

The combination of a silyl-migration from carbon to oxygen and a prototropic isomerization leads to allenyl silyl ethers [246]. 

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