Fig. 2
From: Chiral donor–acceptor azetines as powerful reactants for synthesis of amino acid derivatives

Azetine ring construction. a [3 + 1]-Cycloaddition of methyl 3-triisopropylsil(TIPS)oxy-2-diazo-3-butenoate (1a) with S,S-diphenyl N-(p-chlorophenyl)sulfinylimine (2a) catalyzed by copper(I) tetrakis(acetonitrile). b Asymmetric synthesis of donor–acceptor azetine using copper(I) catalysis with chiral sabox ligand L1.