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The approach is designed on the basis of the key regioselective Diels - Alder reaction of the properly substituted exo - 2 - oxazolidinone diene 3 with acrolein ( 4 ) to give the corresponding adduct 2 .
 Chemical: exo - 2 - oxazolidinone diene; Chemical: acrolein
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: exo - 2 - oxazolidinone diene; Chemical: acrolein