title: Organocatalysis by Networks of Cooperative Hydrogen Bonds: Enantioselective Direct Mannich Addition to Preformed Arylideneureas.
abstract: The concept of noncovalent organocatalysis by means of networks of cooperative hydrogen bonds (NCHB organocatalysis) has been explored. Arylideneureas were chosen as ideal substrates because of their powerful donor-acceptor properties. We have examined their uncatalyzed, direct Mannich reaction with acetoacetates in comparison with that catalyzed by a number of salan derivatives capable of providing a network of cooperative hydrogen bonds. Catalyst D [(R,R)-N,N'-bis(salicyl)cyclohexane-1,2-diamine] was found to drive the above direct Mannich reaction in an enantioselective manner, thereby allowing the synthesis of several Biginelli dihydropyrimidinones with high enantioselectivity. DFT calculations (B3LYP-D-PCM/6-31+G*//B3LYP/6-31+G*) revealed that the NCHB organocatalyst lowers the energy barrier of the reaction. The NCHB organocatalysts appear to function as biomimetic catalysts.
authors.affiliation: Departamento de Química, Universidad de las Islas Baleares, 07122, Palma de Mallorca, Spain.
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Lillo
authors.affiliation: Departamento de Química, Universidad de las Islas Baleares, 07122, Palma de Mallorca, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Mansilla
authors.affiliation: Departamento de Química, Universidad de las Islas Baleares, 07122, Palma de Mallorca, Spain. jmsaa@uib.es.
authors.forename: José M
authors.identifier: http://orcid.org/0000-0001-7365-6690
authors.initials: JM
authors.lastname: Saá
keywords: Mannich reaction; asymmetric catalysis; cooperative hydrogen bonds; dihydropyrimidinones; organocatalysis