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Of the acid labile group R 6 , preferred are alkoxymethyl groups having the formula (e2): 

<img src='content_image/897215.jpg'>

wherein Re is a straight, branched or cyclic C$_{1 }$-C$_{20 }$monova- lent hydrocarbon group such as alkyl. 

Examples of the acid labile group of formula (e2) are shown below, but not limited thereto. 

<img src='content_image/897216.jpg'>

-continued 

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-continued 

