Of the acid labile groups having formula (L4), groups  having the following formulas (L4-1) to (L4-4) are preferred.  38  US 8,968,979 B2  37  In formulas (L4-1) to (L4-4), the broken line denotes a  bonding site and direction. RL 41  is each independently a  monovalent  hydrocarbon  group,  typically  a  straight,  branched or cyclic C$_{1 }$-C$_{10 }$alkyl group, such as methyl, ethyl,  propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl,  n-pentyl, n-hexyl, cyclopentyl and cyclohexyl.  For formulas (L4-1) to (L4-4), there can exist enantiomers  and diastereomers. Each of formulae (L4-1) to (L4-4) collec› tively represents all such stereoisomers. Such stereoisomers  may be used alone or in admixture.  For example, the general formula (L4-3) represents one or  a mixture of two selected from groups having the following  general formulas (L4-3-l) and (L4-3-2).  Examples of the acid labile groups of formula (L2) include  tert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amy- loxycarbony I, tert-amy loxycarbony !methyl, 1, 1-diethy lpro- py loxycarbony I,  1, 1-diethy lpropyloxycarbony lmethy I,  1-ethylcyclopentyloxycarbonyl,  1-ethylcyclopentyloxycar› bonylmethyl, l-ethyl-2-cyclopentenyloxycarbonyl, l-ethyl- 2-cyclopenteny loxycarbony lmethy I, 1-ethoxyethoxycarbon- y lmethy I,  2-tetrahydropyrany loxycarbony !methyl,  and  2-tetrahydrofuranyloxycarbonylmethyl groups.  Examples of the acid labile groups of formula (L3) include  1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclo- pentyl, 1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec› buty lcyclopenty I, 1-cyclohexy lcyclopenty I, 1-( 4-methoxy› buty l)cyclopentyl,  l-(bicyclo[2.2.1 ]heptan-2-yl)  cyclopentyl, l-(7-oxabicyclo[2.2.1 ]heptan-2-yl)cyclopentyl,  1-methylcyclohexyl, 1-ethylcyclohexyl, l-methyl-2-cyclo- penteny I,  1-ethy 1-2-cyclopenteny I,  1-methy 1-2-cyclohex› eny l, and l-ethyl-2-cyclohexenyl groups.  Similarly, the general formula (L4-4) represents one or a  mixture of two or more selected from groups having the  following general formulas (L4-4-1) to (L4-4-4).  (L4-3-2)  (L4-3-1)  (L4-1)  (L4-2)  (L4-3)  (L4-4) 