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This short review summarizes catalytic asymmetric synthesis of gamma - butenolides through direct vinylogous reactions by metal complexes and organocatalysts .
 Chemical: gamma - butenolides
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: gamma - butenolides