| http://www.w3.org/ns/prov#value | - According to a further feature of the present invention, compounds of formula I, wherein R1, R2, R3, Z, Z1 and Z2, are as hereinbefore defined, Z3 represents a --CZCH2 -- linkage, and preferably those wherein Z represents oxygen, are prepared from compounds of formula VII ##STR16## wherein R1, R2, Z, Z1 and Z2 are as hereinbefore defined and R4 and R5 represent lower alkyl, e.g. methyl, groups, by
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