title: Highly diastereoselective one-pot synthesis of spiro[cyclopenta[a]indene-2,2'-indene]diones from 1-indanones and aromatic aldehydes.
abstract: Treatment of 1-indanones with aromatic aldehydes and NaOEt in THF affords complex spiropolycyclic compounds through a four-component reaction in which two molecules of each starting compound are combined with formation of four new carbon-carbon bonds, leading to the elaboration of a new five-membered ring that bears five contiguous stereogenic centers with a well-defined relative configuration. Different amounts of a minor epimer of the main product are also formed. The presence of methoxy substituents in the indanone component and the use of aldehydes derived from pi-excedent heterocycles make the dimerization step a slower transformation. In these cases, better yields of spirodimers are obtained starting from the preformed enones. The reaction seems to take place by cross-aldol condensation, dehydration, and dimerization of the thus formed enones. The molecular mechanism of the dimerization reaction of enone 5g has been studied using DFT methods at the B3LYP/6-31G level. The dimerization takes place through a process involving a Michael addition of a carbanion, obtained by deprotonation of 5g at the 3-position, to a second molecule of 5g, followed by an intramolecular Michael addition in the corresponding intermediate. The final protonation of the resulting anion accounts for the formation of the cis-fused pentacyclic system.
authors.affiliation: Laboratori de Química Farmacèutica (Unitat Associada al CSIC), Facultat de Farmàcia, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Spain. camps@ub.edu
authors.forename: Pelayo
authors.initials: P
authors.lastname: Camps
authors.forename: Luis R
authors.initials: LR
authors.lastname: Domingo
authors.forename: Xavier
authors.initials: X
authors.lastname: Formosa
authors.forename: Carles
authors.initials: C
authors.lastname: Galdeano
authors.forename: Diana
authors.initials: D
authors.lastname: Gonzalez
authors.forename: Diego
authors.initials: D
authors.lastname: Muñoz-Torrero
authors.forename: Sílvia
authors.initials: S
authors.lastname: Segalés
authors.forename: Mercè
authors.initials: M
authors.lastname: Font-Bardia
authors.forename: Xavier
authors.initials: X
authors.lastname: Solans
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D019281:Dimerization; D007189:Indans / Q000737:chemistry; D007192:Indenes / Q000138:chemical synthesis*; D013141:Spiro Compounds / Q000138:chemical synthesis*; D013237:Stereoisomerism
chemical_list: D000447:Aldehydes; D007189:Indans; D007192:Indenes; D013141:Spiro Compounds; C013352:indacrinone