Asymmetric diels-alder reactions of chiral alkoxy iminium salts

✍ Scribed by Michael E. Jung; Wayne D. Vaccaro; Keith R. Buszek

• Publisher: Elsevier Science
• Year: 1989
• Tongue: French
• Weight: 335 KB
• Volume: 30
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)99606-0

✦ Synopsis

The optically active vinyl trimethylsilyloxy iminium salts, prepared from 8 and 14ab, were reacted with cyclopentadiene to give the optically active amides 15 and 16ab in high yield and with good diastereoselectivity.

A major goal in synthetic organic chemistry today is the easy and efficient production of optically active materials from prochiral precursors by asymmetric induction. 2 Several recent publications3 have prompted us to report our preliminary results regarding the Diels-Alder reaction of dienopbiles activated by an adjacent positive center.

In 1976, Baum and Viehe reported the first cycloadditions of acetylenic iminium salts such as 1 to afford the cycloadducts 2 in good to excellent yields.4 Hydrolysis of the cycloadducts under mild conditions gave the ester 3. These alkoxy iminium salts exhibit substantially increased reactivity in Diels-Alder reactions. In fact, the alkoxy iminium group was found to be more activating than the corresponding acid chloride, nitrile, aldehyde, amide, or ester group. It occurred to us that a chiral amide such as 4 might allow for asymmetric induction in Diels-Alder reactions. Hydrolysis of the resulting cycloadduct should provide stereoselectively the bicyclic ester 6 and allow recovery of the chiral auxiliary in a single operation. To our knowledge there are no published reports concerning the Diels-Alder 4 NR;= chiral auxiliary 5