Synthesis and Diels-Alder reactions of 2-alkyl-5-methylene-1,3-dioxolan-4-ones and 2-alkyl-3-acyl-5-methylene-1,3-oxazolidin-4-ones: Highly exo and diastereoface selective chiral ketene equivalents

✍ Scribed by William R. Roush; Amy P. Essenfeld; Joseph S. Warmus; Bradley B. Brown

• Publisher: Elsevier Science
• Year: 1989
• Tongue: French
• Weight: 284 KB
• Volume: 30
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)70683-6

✦ Synopsis

Chiral dienophiles l-3 undergo highly exo and diasfereoface selective Die/s-Alder reactions. The Die/s-Alder reactions of 3 are also highly exo selective under Lewis acid catalyzed conditions.

In connection with an ongoing effort in the natural products arena we required a highly diastereoselective chiral ketene equivalent. 3.4 By analogy to the numerous applications of chiral 2-alkyl-I ,3-dioxolan-4-ones and 2-alkyl-3-acyl-l,3-oxazolidin-4-ones in asymmetric synthesis,5 we reasoned that dienophiles such as 1-3 would display a very large diastereofacial bias in both the exo (4) and endo (5) transition states, with the diene approaching the dienophile from the face opposite the bulky acetal substituent.

For these reagents to be maximally useful, however, it is also necessary that they exhibit a significant preference for either exo or endo cycloaddition,