| http://www.w3.org/ns/prov#value | - The compounds of formula (I) in which A is oxygen may be prepared by cyclising a compound of formula (IV): ##STR6## in which R1, R2, R6, R7, X, W and Z are as defined in formula (I), and R8 is an alkyl group, preferably C1-6 alkyl such as methyl or ethyl.
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