ChemInform Abstract: Studies in Asymmetric Synthesis. Part 4. Studies in Lewis Acid and LiClO4 (or Nafion-H) Catalyzed Ionic Diels—Alder Reactions of Chiral and Achiral Olefinic Acetals Respectively.

✍ Scribed by R. Kumareswaran; Padma S. Vankar; M. Venkat Ram Reddy; Sangeeta V. Pitre; Raja Roy; Yashwant D. Vankar

• Book ID: 101883548
• Publisher: John Wiley and Sons
• Year: 2010
• Weight: 38 KB
• Volume: 30
• Category: Article
• ISSN: 0931-7597
• DOI: 10.1002/chin.199927044

✦ Synopsis

Studies in Asymmetric Synthesis. Part 4. Studies in Lewis Acid and LiClO 4 (or Nafion-H) Catalyzed Ionic Diels-Alder Reactions of Chiral and Achiral Olefinic Acetals Respectively.

-Chiral acetals (I), derived from crotonaldehyde, undergo cycloadditions with isoprene or cyclopentadiene to give the corresponding cycloadducts with moderate to good diastereoselectivity. Compared with previous studies, the use of these chiral acetals shows no improvement of selectivity. Among the tested catalysts, TiCl 2 (O-iPr) 2 gives the best results in terms of yield and stereoselectivity. The 2-endo acetal diastereomers of norbornenes (V), obtained as mixture of diastereomers (54-78% d.e.), are formed with 20-50% excess over the 2-exo acetals. It is found that nitromethane is an ideal solvent for the LiClO 4 catalyzed cycloadditions of achiral acetals. The usefulness of Nafion-H as excellent solid acid catalyst in CH 2 Cl 2 is also demonstrated for a variety of achiral acetals.