N1–C4 β-Lactam Bond Cleavage in the 2-(Trimethylsilyl)thiazole Addition to β-Lactam Aldehydes: Asymmetric Synthesis of Spiranic and Tertiary α-Alkoxy-γ-keto Acid Derivatives

Starting substrates, enantiopure spiranic or 3-substituted 3-alkoxy-4-oxoazetidine-2-carbaldehydes, were prepared from (R)-2,3-O-isopropylideneglyceraldehyde derived azetidine-2,3-diones by sequential Barbier-type addition reactions followed by hydroxy functionalization and aldehyde unmasking. The reaction between the above β-lactam aldehydes and 2-(trimethylsilyl)thiazole (TMST) gave as major products conformationally constrained α-alkoxy-γ-keto amides, which can be considered both as aldols as well as Passerini-type products, by N1–C4 β-lactam bond cleavage. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)