Three-Component Reactions of Diazoesters, Aldehydes, and Imines Using a Dual Catalytic System Consisting of a Rhodium(II) Complex and a Lewis Acid

A dual catalytic system, dirhodium tetrapivalate/ytterbium(III) triflate, enables the three-component reactions of α-alkyl-α-diazoesters, aromatic aldehydes, and N-benzylidenebenzylamine derivatives to afford the corresponding β-amino alcohols in good yields after hydrolysis of the oxazolidine cycloadducts, whereas no β-amino alcohols are obtained in the absence of ytterbium(III) triflate. A similar dual catalytic system, dirhodium tetraacetate/ytterbium(III) triflate, is found to be effective in accelerating the reactions of α-aryl-α-diazoesters in high yields. Furthermore, the reactions using dimethyl diazomalonate are described.

Chiral 2,6-Bis(oxazolinyl)pyridine−Rare Earth Metal Complexes as Catalysts for Highly Enantioselective 1,3-Dipolar Cycloaddition Reactions of 2-Benzopyrylium-4-olates

Significant levels of enantioselectivity were obtained in 1,3-dipolar cycloadditions of 2-benzopyrylium-4-olate generated from the Rh(2)(OAc)(4)-catalyzed decomposition of o-methoxycarbonyl-alpha-diazoacetophenone. This reaction utilized chiral 2,6-bis(oxazolinyl)pyridine (Pybox)--rare earth metal triflate complexes as chiral Lewis acid catalysts. The reactions with several benzyloxyacetaldehyde derivatives catalyzed by a Sc(III)--Pybox-i-Pr complex (10 mol %) proceeded smoothly to yield endo-adducts selectively with high enantioselectivity (up to 93% ee). For the reaction with benzyl pyruvate, the Sc(III)-Pybox-i-Pr complex (10 mol %) catalyzed the reaction effectively in the presence of trifluoroacetic acid (10 mol %) to yield an exo-adduct with both high diastereo- and enantioselectivity (94% ee). This catalytic system was efficiently applied to the reactions with several other alpha-keto esters with high exo- and enantioselectivities (up to 95% ee). In contrast to the reaction with carbonyl compounds, Yb(III)--Pybox-Ph complex (10 mol %) was found to be effective to obtain high enantioselectivity (96% ee) of diastereoselectively produced exo-cycloadduct in the reaction with 3-acryloyl-2-oxazolidinone.

Ruthenium(II) porphyrin catalyzed tandem carbonyl ylide formation and 1,3-dipolar cycloaddition reactions of alpha-diazo ketones

[reaction: see text] The ruthenium porphyrin-catalyzed reactions of diazo ketones with pi-unsaturated compounds via carbonyl ylide formation/cycloaddition cascade exhibit product yields and selectivities comparable to the analogous reactions with dirhodium carboxylates as catalysts. By grafting a ruthenium porphyrin on poly(ethylene glycol) (Zhang, J.-L.; Che, C.-M. Org. Lett. 2002, 4, 1911), a recyclable catalytic system is developed with over 5700 product turnovers attained for the reaction of 1-diazo-2,5-hexanedione with dimethyl acetylenedicarboxylate.

Stereocontrol in rare earth metal triflate-catalyzed 1,3-dipolar cycloaddition reaction of 2-benzopyrylium-4-olate with aldehydes

Exo-cycloadduct was obtained with high stereoselectivity by the addition of ytterbium triflate (Yb(OTf)(3)) (10 mol %) in the rhodium(II) acetate (Rh(2)(OAc)(4))-catalyzed decomposition of o-(methoxycarbonyl)-alpha-diazoacetophenone in the presence of benzaldehyde. In the reaction in the absence of Yb(OTf)(3), almost no selectivity was obtained. Stereoselectivity in the reactions with p-nitrobenzaldehyde, p-anisaldehyde, and benzyloxyacetaldehyde could be also controlled to high exo preference by the addition of Yb(OTf)(3).