Tetrahydroisoquinoline-Based N-Oxides as Chiral Organocatalysts for the Asymmetric Allylation of Aldehydes

Chiral phosphoric acid-catalyzed enantioselective phosphinylation of 3,4-dihydroisoquinolines with diarylphosphine oxides

Chiral phosphorous-containing compounds are playing a more and more significant role in several different research fields. Here, we show a chiral phosphoric acid-catalyzed enantioselective phosphinylation of 3,4-dihydroisoquinolines with diarylphosphine oxides for the efficient and practical construction of a family of chiral α-amino diarylphosphine oxides with a diverse range of functional groups. The phosphine products are suitable for transforming to several kinds of chiral (thio)ureas, which might be employed as chiral ligands or catalysts with potential applications in asymmetric catalysis. Control and NMR tracking experiments show that the reaction proceeds via the tert-butyl 1-(tert-butoxy)-3,4-dihydroiso-quinoline-2(1H)-carboxylate intermediate, followed by C-P bond formation. Furthermore, computational studies elucidated that the hydrogen bonding strength between the phosphonate and isoquinolinium determines the stereoselectivity of the phosphinylation reaction.

MnO2 as a terminal oxidant in Wacker oxidation of homoallyl alcohols and terminal olefins

Efficient and mild reaction conditions for Wacker-type oxidation of terminal olefins of less explored homoallyl alcohols to β-hydroxy-methyl ketones have been developed by using a Pd(ii) catalyst and MnO2 as a co-oxidant. The method involves mild reaction conditions and shows good functional group compatibility along with high regio- and chemoselectivity. While our earlier system of PdCl2/CrO3/HCl produced α,β-unsaturated ketones from homoallyl alcohols, the present method provided orthogonally the β-hydroxy-methyl ketones. No overoxidation or elimination of benzylic and/or β-hydroxy groups was observed. The method could be extended to the oxidation of simple terminal olefins as well, to methyl ketones, displaying its versatility. An application to the regioselective synthesis of gingerol is demonstrated.

Stereoselective synthesis of 1,3-disubstituted dihydroisoquinolines vial-phenylalanine-derived dihydroisoquinoline N-oxides

The preparation of chiral pool-derived nitrone 3 and its use in the protecting-group free, stereoselective synthesis of a range of 1,3-disubstituted tetrahydroisoquinolines is described. Grignard reagent additions to nitrone 3 yielded trans-1,3-disubstituted N-hydroxytetrahydroisoquinolines 6 with good levels of selectivity, while 1,3-dipolar cycloadditions to this nitrone provided access to 3-(2-hydroxyalkyl)isoquinolines 12 as single diastereomers.

Crystal structure of (S)-benzyl 3-(benzylcarba-moyl)-3,4-dihydroisoquinoline-2(1H)-carboxylate, C25H24N2O3

C25H24N2O3, monoclinic, P21 (no. 4), a = 9.7404(5) Å, b = 10.0985(5) Å, c = 10.7520(5) Å, β = 98.328(3)°, V = 1046.45(9) Å3, Z = 2, R gt(F) = 0.0252, wRref(F2) = 0.0600, T = 100 K.

Novel strategies for catalytic asymmetric synthesis of C1-chiral 1,2,3,4-tetrahydroisoquinolines and 3,4-dihydrotetrahydroisoquinolines

This review summarizes recent progress in catalytic asymmetric construction of 1,2,3,4-tetrahydroisoquinolines and 3,4-dihydroisoquinolines, among the most important “privileged scaffolds”.

(S)-Methyl 3-(3,4-dimethoxyphenyl)-2-[2-(diphenylphosphanyl)benzamido]propanoate

Mol­ecules of the title compound, C₃₁H₃₀NO₅P, show a sttagered conformation about the C—C bond joining the dimeth­oxy­benzene group to the chiral centre, with the dimeth­oxy­benzene ring gauche to the amide group and anti to the ester group. In the crystal, weak inter­molecular N—H⋯O and C—H⋯O hydrogen bonds form layers parallel to (110).