No abstract

No abstract

No abstract

(2S,4R)‐4‐Hydroxyproline has been anchored to the monomethyl ether of poly(ethylene glycol), MW 5000, by means of a succinate spacer to afford a soluble, polymer‐supported catalyst (PEG‐Pro) for enantioselective aldol and iminoaldol condensation reactions. This organic catalyst can be considered as a minimalistic version of a type I aldolase enzyme, with the polymer chain replacing the enzyme's peptide backbone, and the proline residue acting as the enzyme's active site. In the presence of PEG‐Pro (0.25–0.35 mol equiv.), acetone reacted with enolizable and non‐enolizable aldehydes and imines to afford β‐ketols and β‐aminoketones in good yield and high enantiomeric excess (ee), comparable to those obtained using non‐supported proline derivatives as the catalysts. Extension of the PEG‐Pro‐promoted condensation to hydroxyacetone as the aldol donor opened an access to synthetically relevant anti‐α,β‐dihydroxyketones and syn‐α‐hydroxy‐β‐aminoketones, that were obtained in moderate to good yields, and good to high diastereo‐ and enantioselectivity. Exploiting its solubility properties, the PEG‐Pro catalyst was easily recovered and recycled to promote all of the above‐mentioned reactions, that occurred in slowly diminishing yields but virtually unchanged ee's.

The stereoselective addition of aryl- and alkylacetylene derivatives to imines was studied. The reaction is catalyzed by copper complexes of enantiomerically pure bisimines, readily prepared in very high yields from the commercially available binaphthyl diamine. A very simple experimental procedure allowed to obtain at room temperature optically active propargylamines in high yields and enantioselectivity. Interestingly, bisimine/copper(I) complexes were able to promote the direct, enantioselective, catalytic addition to imines of alkylacetylenes. The effects of catalyst loading and other reaction parameters on the stereochemical outcome of the transformation were investigated. The extremely convenient methodology, the mild reaction conditions, and the possibility of a modular approach for developing new and more efficient bisimine-based chiral ligands make the present methodology very attractive.

No abstract

No abstract

[structure: see text]. 1,1'-Binaphthyl-2,2'-diamine-based (S)-prolinamides in the presence of stearic acid were able to promote the direct aldol condensation of cyclohexanone and other ketones with different aldehydes in the presence of a massive amount of water in very good yields, high diastereoselectivity, and up to 99% ee. The behavior of both C2- and C1-symmetric catalysts in combination with different additives was investigated, and a preliminary experiment of recovering and recycling of the catalytic system was also attempted.