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Stereoselective synthesis of Gly-Gly-type (E)-methylalkene and (Z)-chloroalkene dipeptide isosteres and their application to 14-mer RGG peptidomimetics

H. Okita, Y. Kato, T. Masuzawa, K. Arai, S. Takeo, K. Sato, N. Mase T. Oyoshi and T. Narumi*

RSC Adv., 2020, 10, 29373-29377.

Stereoselective and efficient synthesis of Gly-Gly-type (E)-methylalkene and (Z)-chloroalkene dipeptide isosteres is realized by organocuprate-mediated single electron transfer reduction. The synthetic isosteres can be used in Fmoc-based solid phase peptide synthesis, resulting in the preparation of the 14-mer RGG peptidomimetics containing an (E)-methylalkene or a (Z)-chloroalkene unit.

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 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.