Catalytic asymmetric synthesis of beta-sultams as precursors for taurine derivatives.
Beta-sultams, biologically interesting sulfonyl analogues of beta-lactams, have been prepared by an organocatalytic asymmetric formal [2+2]-cycloaddition approach of non-nucleophilic imines with alkyl sulfonyl chlorides. In the case of very electron poor N-tosyl imines derived from chloral or ethylglyoxylate, this reaction type was catalyzed by cinchona alkaloids providing the heterocycles in high yield, with good diastereoselectivity and up to 94% ee. Mechanistic investigations suggested that the product formation proceeded via a zwitterionic imine-catalyst adduct. The scope was significantly extended by 2-pyridylsulfonyl imines derived from non-activated aromatic aldehydes employing Yb(OTf)3 as Lewis acid cocatalyst. The synthetic value of the strained enantioenriched beta-sultams was demonstrated by smooth nucleophilic ring opening reactions with O-, N- and C-nucleophiles yielding a variety of acyclic beta-aminosulfonyl (taurine) derivatives (sulfonates, sulfonamides, sulfones) without racemization or epimerization.
Zajac
Marian
M
ETH Zürich, Hönggerberg, Laboratory of Organic Chemistry, Wolfgang-Pauli-Str. 10, 8093 Zürich, Switzerland.
Peters
René
R
D002384:Catalysis; D007097:Imines / Q000737:chemistry; D015394:Molecular Structure; D013237:Stereoisomerism; D013449:Sulfonamides / Q000138:chemical synthesis* / Q000737:chemistry; D013654:Taurine / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry; D015018:Ytterbium / Q000737:chemistry; D047090:beta-Lactams / Q000138:chemical synthesis* / Q000737:chemistry
D007097:Imines; D013449:Sulfonamides; D047090:beta-Lactams; C480101:beta-sultam; D013654:Taurine; D015018:Ytterbium