Synthesis of functionalized chromene and spirochromenes using l-proline-melamine as highly efficient and recyclable homogeneous catalyst at room temperature

• Published in: Tetrahedron letters Vol. 58; no. 44; pp. 4200 - 4204
• Main Authors: Nagaraju, Sakkani, Paplal, Banoth, Sathish, Kota, Giri, Santanab, Kashinath, Dhurke
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-11-2017
• Subjects: 4H-chromene; Homogeneous catalysis; l-Proline; Melamine; Recyclable catalyst; Spirooxindole; Recyclable catalyst; Spirooxindole; Melamine; l-Proline; 4H-chromene; Homogeneous catalysis
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2017.09.060

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•Highly efficient and recyclable homogeneous catalyst.•α-Amino acids and aromatic amines as donor-acceptor pairs.•Catalyst recovery and reuse up to 6 cycles.•Efficient for 8 types of nucleophiles.
An efficient and recyclable homogeneous catalyst is developed using commercially cheap l-proline and melamine for the synthesis of chromenes and spirochromenes (spirooxindoles) via multicomponent reactions at room temperature. Systematic studies were conducted in order to achieve desired reactivity and recyclability of the catalyst using various α-amino acids and aromatic amines as donor-acceptor pairs. Among the screened combinations, l-proline and melamine (3:1 ratio; 3mol% on total weight) was found to be best catalyst to give the desired products with excellent yields (up to 99%) in very short times (1–15min) at room temperature in DMSO as solvent. The catalyst was recovered by adding EtOAc and reused up to 5 cycles without losing the catalytic activity.