Reductive ring cleavage of 1‐alkyl‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinones with raney‐nickel alloy. Synthesis of <i>N</i>‐benzoyl‐3‐alkylamino‐3‐phenylalanine amides from <i>rel</i>‐(4<i>R</i>,5<i>R</i>)‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinone

Abstract

Abstract rel ‐(4 R ,5 R )‐4‐Benzoylamino‐5‐phenyl‐3‐pyrazolidinone ( 1 ) was alkylated at position 1 with carbonyl compounds 2a‐g . The corresponding rel ‐(4 R ,5 R )‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinone‐1‐azomethine imines 3a‐g , were treated with sodium borohydride to give rel ‐(4 R ,5 R )‐1‐alkyl‐4‐benzoylamino‐5‐phenyl‐3‐pyrazolidinones 4a‐g . Reduction of pyrazolidinones 4a‐g with Raney‐nickel alloy in methanolic potassium hydroxide furnished rel ‐(4 R ,5 R )‐ N ‐benzoyl‐3‐alkylamino‐3‐phenylalanine amides 5a‐f .