A highly enantioselective organocatalytic vinylogous Mukaiyama aldol reaction of silyloxy dienes and isatins under bifunctional organocatalysis is presented. Substituted 3-hydroxy-2-oxindoles are synthesised in good yields and enantioselectivities. These synthetic intermediates are used for the construction of more complex molecules with biological properties such as the formal synthesis of a CB2 agonist presented.
An enantioselective organocatalytic conjugate azidation of α,β‐unsaturated ketones is presented. A bifunctional organocatalyst activates TMSN3, triggering the nucleophilic addition of the azido group to enones in absence of external promoters and avoiding the direct use or the pre‐formation of highly toxic and explosive hydrazoic acid. This protocol proceeds with excellent enantiocontrol under mild conditions. DFT calculations and mechanistic trials have been performed in order to demonstrate the direct activation performed by the bifunctional organocatalyst.magnified image
A highly
efficient enantioselective inverse-electron-demand aza-Diels–Alder
reaction between aza-sulfonyl-1-aza-1,3-butadienes and silyl (di)enol
ethers has been developed. The presented methodology allows the synthesis
of benzofuran-fused 2-piperidinol derivatives with three contiguous
stereocenters in a highly selective manner, as even the hemiaminal
center is completely stereocontrolled. Density functional theory (DFT)
calculations support that the hydrogen-bond donor-based bifunctional
organocatalyst selectively triggers the reaction through the ipso,α-position
of the dienophile, in contrast to the reactivity observed for dienolates
in situ generated from β,γ-unsaturated derivatives. Moreover,
the calculations have clarified the mechanism of the reaction and
the ability of the hydrogen-bond donor core to hydrolyze selectively
the
E
isomer of the dienol ether. Furthermore, to
demonstrate the applicability of silyl enol ethers as nucleophiles
in the asymmetric synthesis of interesting benzofuran-fused derivatives,
the catalytic system has also been implemented for the highly efficient
installation of an aromatic ring in the piperidine adducts.
A highly regio- and enantioselective vinylogous Mukaiyama-type reaction for the dearomatization of quinazolines and other heteroarenes under anion-binding catalysis is presented.
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