prov:value
| - R3 is a carbonyl substituted with hydrogen, hydroxyl, trialkylsilyl, trialkylsiloxy, C1-30 alkyl, C7-30 aralkyl, C1-30 alkoxy, C1-30 amine (primary, secondary or tertiary), C1-30 thiol; C6-20 aryl; C1-20 alkenyl; C1-20 alkynyl; 1,2-dicarbonyl, such as ##STR5## substituted with C1-6 alkyl or C6-20 aryl; anyhdrides such as ##STR6## substituted with C1-6 alkyl or C6-20 aryl; azomethine substituted at
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