prov:value
| - Another embodiment of the invention involves compounds of the formula Ib: ##STR6## where at least one of R', R and R' is other than H and each independently represents halo, phenyl, substituted phenyl, hydroxy, mercapto, alkyl of 2 to 6 carbon atoms, alkyl--C(O)--, alkyl substituted with a hydroxy or CF3 ; R3 and R4 are the same or different and are as defined above, preferably H or halo, e.g.,
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