10517
The key step in this synthesis is a highly diastereoselective ethylation at the C20 position by using N - arylsulfonyl - ( R ) - 1 , 2 , 3 , 4 - tetrahydroisoquinoline - 3 - carboxylic acid ester as a chiral auxiliary , which affords the key intermediate ethyl - ( S ) - 2 - acyloxy - 2 - ( 6 - cyano - 5 - oxo - 1 , 2 , 3 , 5 - tetrahydroindolizin - 7 - yl ) butanoate ( 8k ) in 93 % yield and 87 % de .
 Chemical: N - arylsulfonyl - ( R ) - 1 , 2 , 3 , 4 - tetrahydroisoquinoline - 3 - carboxylic acid ester; Chemical: ethyl - ( S ) - 2 - acyloxy - 2 - ( 6 - cyano - 5 - oxo - 1 , 2 , 3 , 5 - tetrahydroindolizin - 7 - yl ) butanoate
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: N - arylsulfonyl - ( R ) - 1 , 2 , 3 , 4 - tetrahydroisoquinoline - 3 - carboxylic acid ester; Chemical: ethyl - ( S ) - 2 - acyloxy - 2 - ( 6 - cyano - 5 - oxo - 1 , 2 , 3 , 5 - tetrahydroindolizin - 7 - yl ) butanoate