Total Synthesis of (+)-Alexine by Utilizing a Highly Stereoselective [3+2] Annulation Reaction of an N-Tosyl-α-Amino Aldehyde and a 1,3-Bis(silyl)propene

✍ Scribed by Martina Dressel; Per Restorp; Peter Somfai

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 294 KB
• Volume: 14
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200701776

✦ Synopsis

Abstract

A novel route towards the polyhydroxylated pyrrolizidine alkaloid (+)‐alexine has been developed. A key step in this synthesis is a highly stereoselective [3+2] annulation reaction of N‐Ts‐α‐amino aldehyde 7 a (Ts=tosyl) and 1,3‐bis(silyl)propene 8 a for the construction of the polyhydroxylated pyrrolidine subunit of the target molecule. Previous synthetic strategies rely on carbohydrates that require several protecting‐group manipulations, thereby making the total number of steps relatively high. The [3+2] annulation strategy compares favorably with carbohydrate‐based syntheses and constitutes a highly efficient entry to polyhydroxylated alkaloids.