Economic and environmentally friendly bio-mimetic one-pot three and four-component Knoevenagel–hydrogenation (K–H), five-component Knoevenagel–hydrogenation– alkylation (K–H–A) and six-component Knoevenagel–hydrogenation–alkylation–Huisgen cycloaddition (K–H–A–HC) reactions of aldehydes, CH-acids, o-phenylenediamine, alkyl halides and azides using proline, proline–metal carbonate and proline–metal carbonate– ...