The stereochemistry of the addition of titanium enolates of N-propionyl-oxazolidin-2-ones to 5- and 6-membered N-acyliminium ions

• Published in: Tetrahedron letters Vol. 40; no. 15; pp. 2891 - 2894
• Main Authors: Pilli, Ronaldo A., de Fátima Alves, Conceição, Böckelmann, Maria Alice, Mascarenhas, Yvonne P., Geraldo Nery, J., Vencato, Ivo
• Format: Journal Article
• Language: English
• Published: OXFORD Elsevier Ltd 09.04.1999; Elsevier
• Subjects: 2-substituted pyrrolidines and piperidines; Chemistry; Chemistry, Organic; N-acyliminium ion; Physical Sciences; Science & Technology; Titanium enolates; β-amino acid derivatives; 2-substituted pyrrolidines and piperidines; Titanium enolates; N-acyliminium ion; β-amino acid derivatives; titanium enolates; beta-amino acid derivatives; BETA-AMINO ACIDS; 2-substituted pyrrolidines and piperidine
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/S0040-4039(99)00398-6

The stereochemistry of the addition of the N-propionyl titanium enolates 2a and 2b to 5- and 6-membered 2-ethoxycarbamates 1a-f was investigated. The addition proceeded stereoselectively to afford the corresponding ( 2S,1′S)-2-substituted pyrrolidines as the major diastereoisomer. Despite the lack of reactivity between 2-ethoxypiperidines 1b and N-propionyl titanium enolates 2a and 2b, less bulky carbamate groups on 2-ethoxypiperidines 1d and 1f restored reactivity and the corresponding 2-substituted piperidines were obtained in moderate to good yields although with poor diastereoselection. Graphic