An enantioselective (3+2) cycloaddition via N-heterocyclic carbene-catalyzed homoenolate addition to cyclic N-sulfonyl trifluoromethyl ketimines is realized, affording fused N-heterocycle γ-lactams with up to >20 : 1 dr and 94–99% ee.
Herein,
we report a highly efficient organocatalytic asymmetric
synthesis of axially chiral biaryl phosphonates with p-quinone phosphonates and 2-naphthols via CPA-catalyzed asymmetric
arylations. A series of chiral biaryl monophosphonates were obtained
in excellent yields and enantioselectivities (up to 99% yield and
95% ee). This reaction could be operated at a gram scale with a low
catalyst loading (0.5 mol %). Remarkably, our approach provides a
green and ready access to chiral biaryl monophosphorus ligands. Compound 4ca was successfully converted to novel chiral biaryl monophosphorus
ligands 7a, 7b, and 8 with
high enantioselectivities in three steps.
Highly enantioselective Mannich addition reactions of N,S‐heterocyclic dibenzo[b,f][1,4]thiazepines as seven‐membered cyclic imine substrates with ketones were developed by using proline as an organocatalyst. Substituted dibenzo[b,f][1,4]thiazepines and various unsymmetrical alkyl methyl ketones were used as substrates and optimized reaction conditions offered an efficient method to synthesize optically active 11‐substituted 10,11‐dihydrodibenzo[b,f][1,4]thiazepine derivatives that contained a carbonyl functional group in 91–99 % ee. Furthermore, we found that the reactions could also be performed on a gram scale, whilst maintaining high yields and enantioselectivities. The carbonyl group of the Mannich products also underwent diastereoselective reduction, thus yielding a new hydroxy‐substituted chiral stereogenic center with moderate‐to‐excellent diastereoselectivities, good yields, and without the loss of enantiomeric excess.
A new type of spirocyclic bisoxindole-based
C2-symmetric
diols (SBIDOLs) was designed and synthesized. A series of racemic
SBIDOL derivatives (6a–6g) were readily synthesized
from commercially available 2-halo-5-methoxyanilines 1 (X = Cl or Br) through N-mono alkylation, acylation, oxidation,
double intramolecular Friedel–Crafts reaction, and demethylation
reactions. The optical resolution of racemic 6b was achieved
via fractional crystallization of their bis-l-menthoxycarboxylates.
Further modifications of SBIDOLs were investigated, leading to 5,5′-diaryl
SBIDOL derivatives (11a and 11b) through
Pd-catalyzed Suzuki coupling and DM-SBIDOL 12 by Pd/C-catalyzed
hydrogenative dechlorination reactions.
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