カテゴリー: Publication

Pendant Alkoxy Groups Drive the Efficiency of NHC Catalyst

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Pendant Alkoxy Groups on N-Aryl Substitutions Drive the Efficiency of Imidazolylidene Catalysts for Homoenolate Annulation from Enal and Aldehyde

R. Kyan, K. Sato, N. Mase and T. Narumi*

Angew. Chem. Int. Ed. 2020, 59, 19031–19036.

The formation of conjugated Breslow intermediate is a turnover-limiting step in the NHC-catalyzed γ-butyrolactone formation via homoenolate addition. Structural and mechanistic studies including deuterium exchange experiments revealed that the formation of conjugated Breslow intermediate is facilitated by the proximity effects of pendant alkoxy groups on ortho-N-aryl groups of imidazolylidene catalyst.

Chemoselective Umpolung Catalyzed by NHC

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Chemoselective Umpolung of Enals for Asymmetric Homoenolate Cross-Annulation of Enals and Aldehydes Catalyzed by N-Heterocyclic Carbene

R. Ide, R. Kyan, T. P. Le, Y. Kitagawa, K. Sato, N. Mase and T. Narumi*

Org. Lett. 2019, 21, 22, 9119–9123.

An asymmetric homoenolate cross-annulation of enals and aldehydes with high enantioselectivity is realized by NHC-catalyzed chemoselective umpolung of enals. The reaction proceeds in a highly chemoselective manner, selectively generating the conjugated Breslow intermediates from enals rather than aldehydes, enabling the homoenolate addition of enals to aldehydes in preference to competing acyl anion-mediated reactions. Enantioenriched substituted γ-butyrolactones are formed in good yields with high enantioselectivities.

Methodology: Chloroalkene’s Powerful Potentials

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Improvement of chemical stability of conjugated dienes by chlorine substitution

T. Narumi*, T. Nishizawa, T. Imai, R. Kyan, H. Taniguchi, K. Sato, N. Mase

Tetrahedron, 2018, 74 (45) 6527-6533.

Conjugated systems have versatile utilities in various fields including organic synthesis, pharmaceutical development, and material science. Such systems take advantage of their properties, which include their unique reactivity, relatively rigid structures, and low HOMO-LUMO gap energies. Their utility and the handling of conjugated systems however are both limited by excessively high photosensitivity and reactivity. We now report a novel molecular approach to the improvement of the chemical stability of the acyclic conjugated system against the photolysis and oxidation reactions simply by the introduction of a chlorine atom into the conjugated system. Systematic studies of substrates with various substituents reveal that the improved chemical stability is based on the additive effects of the steric and electronic properties of the chlorine atom substituent.