Asymmetric dihydroxylation of chiral γ-amino α,β-unsaturated esters: Turning the mismatched into the matched case via protective group tuning

Organocatalytic Sequential α-Amination−Horner−Wadsworth−Emmons Olefination of Aldehydes: Enantioselective Synthesis of γ-Amino-α,β-Unsaturated Esters

A novel and highly enantioselective method for the synthesis of gamma-amino-alpha,beta-unsaturated esters via tandem alpha-amination-Horner-Wadsworth-Emmons (HWE) olefination of aldehydes is described. The one-pot assembly has been demonstrated for the construction of functionalized chiral 2-pyrrolidones, subunits present in several alkaloids. [structure: see text]

Stereoselective synthesis and glycosidase inhibitory activity of 3,4-dihydroxy-pyrrolidin-2-one, 3,4-dihydroxy-piperidin-2-one and 1,2-dihydroxy-pyrrolizidin-3-one

3,4-Dihydroxy-pyrrolidin-2-one, 3,4-dihydroxy-piperidin-2-one and 1,2-dihydroxy-pyrrolizidin-3-one have been synthesized, using a simple strategy based on the asymmetric dihydroxylation of vinylogous aminoesters and subsequent mild intramolecular cyclization. All these compounds show a partial inhibition of alpha-glucosidase, but were inactive towards other glycosidases.

Stereoselective dihydroxylation reactions of γ-amino-α,β-unsaturated esters via their aryl ketimine derivatives

OsO4-catalysed dihydroxylation reactions of the aryl ketimine derivatives of (E)-gamma-amino-alpha,beta-unsaturated esters gave anti selectivity ranging from 6.7 : 1 to 19 : 1, whereas the opposite syn selectivity was consistently observed with those of (Z)-gamma-amino-alpha,beta-unsaturated esters (5.4 : 1 to > 100 : 1).

Diastereoselective Osmylation and Hydroboration of beta,gamma-Unsaturated N,N-Diisopropylamides and Acid-Catalyzed Conversion to delta-Lactones

The title reactions of beta,gamma-unsaturated N,N-diisopropylamides occur with useful diastereofacial selectivity. The major diol isomer from osmylation of alkenes 1, 10, 11, and 12 in the presence of TMEDA at -78 degrees C corresponds to the facial preference shown in transition state model 41 (R(Z) = H), while the opposite preference for 42 is observed with the Z-alkene 13. (Table 1). Hydroboration with 9-BBN does not show this inversion of diastereofacial selectivity for the Z-alkene. All of the results in Table 2 correspond to the usual preference for a transition state such as 45. Acid-catalyzed lactonization of the alcohols obtained in Tables 1 and 2 can be carried out with overall retention of configuration to afford delta-lactones. Butenolide 5 was prepared with 90% ee from alcohol 2a via osmylation followed by acid-catalyzed lactonization to 3 and elimination using SOCl(2)/pyridine.