Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non-C2 -symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity. These compounds have also been prepared in gram quantities and recrystallized to near enantiopurity.
Simple quinine as an organocatalyst mediates the addition of various naphthols to halogenated quinones to afford non‐C2‐symmetrical, axially chiral biaryl products, which are promising compounds as chiral ligands and organocatalysts. The rotational barrier required to have two distinct atropisomers has been evaluated in the products generated from the addition of naphthols to various quinones by means of DFT calculations and HPLC. The use of halogenated quinones as reagents was necessary to have configurationally stable enantiomeric products which can be obtained in good yield and stereoselectivity. These compounds have also been prepared in gram quantities and recrystallized to near enantiopurity.
Click chemistry is used to functionalize simple lipophilic and water-soluble molecules, a complex PEGylated phospholipid (DSPE-PEG2000), and two benzylic substrates with the 2-(hydroxyimino)aldehyde (HIA) group. To this end, two terminal alkynes bearing the HIA moiety were synthesized and coupled to different azides through copper(I)-catalyzed azide alkyne cycloaddition (CuAAC). Norrish-Yang photoisomerization (λ = 365 nm, LED source) is successfully obtained, with no interference by the triazole linker, except when the forbidden n-π* carbonyl transition is screened by a remote substituent such as salicylaldehyde. UV-Vis spectrometry suggests a specific interaction of HIAs with Cu(II), whereas no such evidence is found with Cu(I). We thereby show that the CuAAC methodology can be used successfully to obtain HIA-based UV-responsive hydrophilic or lipophilic ligands, phospholipidic components for the construction of liposomes, and macrocycle precursors.
Benzazetidines are highly strained and inherently unstable heterocycles. There are only few methodologies for assembling these compounds. Here, a protocol is presented to trap an elusive cyclic, 4-membered hemiaminal structure. This method affords several benzazetidine in moderate to good yields (up to 81%), it uses inexpensive materials and does not require catalysts based on transition metals. The high ring strain energy of these benzazetidine systems was estimated by DFT calculations to be about 32 kcal mol-1. This synthesis can be applied also on gram scale with reaction yield essentially unchanged.
A highly stereoselective procedure for the synthesis
of spiro-polycyclic
oxindoles bearing five contiguous stereogenic centers including two
tetrasubstituted carbons has been developed. Under sequential organocatalysis
performed by a pyrrolidine-based organocatalyst and DBU, a highly
atom-economical Michael–domino Michael/aldol reaction sequence
was optimized, yielding variously functionalized spiro-decalin oxindoles
with excellent stereoselectivity (>99:1 dr, up to 92% ee).
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