Abstract:A highly
regio- and diastereoselective method to access cis-2,6-disubstituted dihydropyridinones under mild conditions
by an iridium-catalyzed allylic etherification is reported. cis-2,6-Disubstituted dihydropyridinones are important precursors
for the de novo synthesis of the corresponding piperidine
alkaloids and iminosugars. This strategy features a broad substrate
scope, high yields, and excellent regio- and diastereoselectivities.
A π-allyl-Ir intermediate is involved in the mechanism. The
strong A1,3-str… Show more
“…In addition, the OH group can be successfully converted to ether or sulfide moieties in good yields and excellent enantioselectivities ( 5f , 77% yield, 5:1 dr and >99% ee; 5 g , 76% yield, >19:1 dr and >99% ee. The high diastereoselectivity of product 5 g may be result of the steric effect (See Supplementary Procedures I and J), and its absolute configuration was established through the X-ray diffraction analysis (CCDC 1821791) 63 .Fig. 4Divergent synthetic transformations of chiral hemiaminal 4aq .…”
Catalytic asymmetric cycloadditions via transition-metal-containing dipolar intermediates are a powerful tool for synthesizing chiral heterocycles. However, within the field of palladium catalysis, compared with the well-developed normal electron-demand cycloadditions with electrophilic dipolarophiles, a general strategy for inverse electron-demand ones with nucleophilic dipolarophiles remains elusive, due to the inherent linear selectivity in the key palladium-catalyzed intermolecular allylations. Herein, based on the switched regioselectivity of iridium-catalyzed allylations, we achieved two asymmetric [4+2] cycloadditions of vinyl aminoalcohols with aldehydes and β,γ-unsaturated ketones through synergetic iridium and amine catalysis. The activation of vinyl aminoalcohols by iridium catalysts and carbonyls by amine catalysts provide a foundation for the subsequent asymmetric [4+2] cycloadditions of the resulting iridium-containing 1,4-dipoles and (di)enamine dipolarophiles. The former provides a straightforward route to a diverse set of enantio-enriched hydroquinolines bearing chiral quaternary stereocenters, and the later represent an enantio- and diastereodivergent synthesis of chiral hydroquinolines.
“…In addition, the OH group can be successfully converted to ether or sulfide moieties in good yields and excellent enantioselectivities ( 5f , 77% yield, 5:1 dr and >99% ee; 5 g , 76% yield, >19:1 dr and >99% ee. The high diastereoselectivity of product 5 g may be result of the steric effect (See Supplementary Procedures I and J), and its absolute configuration was established through the X-ray diffraction analysis (CCDC 1821791) 63 .Fig. 4Divergent synthetic transformations of chiral hemiaminal 4aq .…”
Catalytic asymmetric cycloadditions via transition-metal-containing dipolar intermediates are a powerful tool for synthesizing chiral heterocycles. However, within the field of palladium catalysis, compared with the well-developed normal electron-demand cycloadditions with electrophilic dipolarophiles, a general strategy for inverse electron-demand ones with nucleophilic dipolarophiles remains elusive, due to the inherent linear selectivity in the key palladium-catalyzed intermolecular allylations. Herein, based on the switched regioselectivity of iridium-catalyzed allylations, we achieved two asymmetric [4+2] cycloadditions of vinyl aminoalcohols with aldehydes and β,γ-unsaturated ketones through synergetic iridium and amine catalysis. The activation of vinyl aminoalcohols by iridium catalysts and carbonyls by amine catalysts provide a foundation for the subsequent asymmetric [4+2] cycloadditions of the resulting iridium-containing 1,4-dipoles and (di)enamine dipolarophiles. The former provides a straightforward route to a diverse set of enantio-enriched hydroquinolines bearing chiral quaternary stereocenters, and the later represent an enantio- and diastereodivergent synthesis of chiral hydroquinolines.
“…Benzyl mercaptan, as another thiol nucleophile, could site‐selectively attack the olefin of dihydropyranone 3 j to afford tetrahydro‐ β ‐pyrone 6 a in high regio‐ and diastereoselectivity (Scheme 2b). The pseudoaxially oriented substituents at C2’ and C6’ positions of Achmatowicz rearrangement product 3 j supply enough steric hindrance to enforce the equatorial approach of nucleophile, which led to the excellent diastereoselevtivity in this 1,4‐addition [10a] …”
A Pd‐catalyzed C‐glycosylation reaction was developed by allyl‐allyl coupling process using Achmatowicz rearrangement products as donors and methylcoumarins as acceptors under mild conditions. This method featured regio‐ and diastereoselectivities, stereodivergent synthesis of C‐glycosides. The glycosyl donors with controlled stereodiversity and glycosyl acceptors with fluorescent performace further highlighted this methodology.magnified image
A process for the de novo synthesis of imino‐C‐glycosides is described. The methodology is based on the reaction of 1‐C‐stannylated iminosugars with various electrophiles under the conditions of Migita‐Kosugi‐Stille cross‐couplings, which gives 1‐C‐substituted iminosugar derivatives in a stereoretentive process. The required iminoglycosyl stannanes are obtained by way of the highly stereoselective addition of tributylstannyllithium to (SR)‐ or (SS)‐N‐tert‐butanesulfinyl glycosylamines, followed by an activation cyclization sequence. Most interestingly, the methodology is tunable: the configuration of the tin adduct is controlled exclusively by the tert‐butanesulfinyl auxiliary, thus giving access after ring formation to ‘α’‐configured or ‘β’‐configured iminoglycosyl stannanes. With the subsequent stereoretentive C−C bond‐forming process, the methodology allows the synthesis of pseudo anomers of imino‐C‐glycosyl compounds in a controlled fashion.
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