Asymmetric synthesis of polycyclic 3-fluoroalkylproline derivatives by intramolecular azomethine ylide cycloaddition
The asymmetric synthesis of polycyclic fluorinated proline derivatives has been accomplished by means of an intramolecular azomethine ylide cycloaddition with fluorinated dipolarophiles. Thus, the reaction of benzaldehydes bearing a trifluoromethyl alkene in ortho position with an azomethine ylide precursor derived from chiral 2-amino indanol takes place with excellent levels of diastereoselectivity, with simultaneous generation of four stereocenters. In order to determine the influence of the fluorine moiety in the process, starting material bearing non-fluorinated alkenes were synthesised. In this case, a dramatic drop of selectivity occurred, which indicates that the role of the fluorine…
Asymmetric diastereodivergent Michael addition of 2-chloromalonate esters to conjugated imines enabled by catalyst metal change
Despite recent progress in asymmetric diastereodivergent reactions leading to products bearing two stereogenic centers, little research has been devoted to processes were a stereogenic center and a double bond are formed. Here, we report the asymmetric diastereodivergent Michael addition of 2-chloromalonate esters to N-tosyl β,γ-unsaturated α-ketimino esters to give chiral α,β-dehydro-α-aminoesters bearing either a Z or E enamine moiety, using pyBOX-metal complexes. Diastereodivergency is achieved by simply changing the metal ion from a trivalent La(III) to a divalent Ca(II) ion, providing the Z or E enamines. Computational studies reveal the crucial role of London interactions between the …
A molecular electron density theory study of the [3 + 2] cycloaddition reaction of nitrones with ketenes.
The [3 + 2] cycloaddition (32CA) reaction between nitrones and ketenes has been studied within the Molecular Electron Density Theory (MEDT) at the Density Functional Theory (DFT) MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual DFT reactivity indices allows the explanation of the reactivity, and the chemo- and regioselectivity experimentally observed. The particular mechanism of this 32CA reaction involving low electrophilic ketenes has been elucidated by using a bonding evolution theory (BET) study. It is determined that this reaction takes place in one kinetic step only but in a non-concerted manner since two stages are clearly identified. Indeed, the formation of the se…
A DFT study of the molecular mechanisms of the nucleophilic addition of ester-derived lithium enolates and silyl ketene acetals to nitrones: Effects of the lewis acid catalyst
9 pages, 6 schemes, 3 figures, 2 tables.
Organocatalytic enantioselective synthesis of trifluoromethyl-containing tetralin derivatives by sequential (hetero)Michael reaction–intramolecular nitrone cycloaddition
The enantioselective synthesis of tetralin derivatives bearing a trifluoromethylated all‐carbon quaternary stereocenter has been accomplished through a synthetic sequence comprising an organocatalytic β‐functionalization of ortho‐1‐trifluoromethylvinyl‐(hetero)aromatic conjugated aldehydes followed by the intramolecular nitrone 1,3‐cycloaddition reaction (INCR). Both nitromethane and N‐Cbz‐hydroxylamine were employed as nucleophiles in the initial organocatalytic conjugate addition step, which provided the chiral information required for the subsequent diastereoselective INCR. Although diastereoselectivity was moderate, good yields and enantioselectivities were, in general, obtained. Intere…
CCDC 1564495: Experimental Crystal Structure Determination
Related Article: Fernando Rabasa-Alcañiz, Javier Torres, María Sánchez-Roselló, Tomás Tejero, Pedro Merino, Santos Fustero, Carlos del Pozo|2017|Adv.Synth.Catal.|359|3752|doi:10.1002/adsc.201700975
CCDC 1564490: Experimental Crystal Structure Determination
Related Article: Fernando Rabasa-Alcañiz, Javier Torres, María Sánchez-Roselló, Tomás Tejero, Pedro Merino, Santos Fustero, Carlos del Pozo|2017|Adv.Synth.Catal.|359|3752|doi:10.1002/adsc.201700975
CCDC 1899383: Experimental Crystal Structure Determination
Related Article: Fernando Rabasa-Alcañiz, Daniel Hammerl, Anabel Sánchez-Merino, Tomás Tejero, Pedro Merino, Santos Fustero, Carlos del Pozo|2019|Org.Chem.Front.|6|2916|doi:10.1039/C9QO00525K