Catalysis & Methodology

Members: Byungman Kang, Ryan Totten, Yalan Ning, Ye-Seong Kim

Cycloaddition of Aziridines and Heterocummulenes
We have developed the [3+2] cycloaddition of aziridines with dipolarophiles that can provide valuable heterocycles such as oxazolidinones and oxazolidines. The high ring strain of aziridines make them useful precursors to a wide range of functionalized nitrogen-containing compounds. In particular, the cycloadditon of aziridines in the presence of catalytic amount of Lewis acid is an attractive and practical alternative to the existing preparation of heterocycles. We are currently focusing on the development of asymmetric cycloadditions that are synthetically useful and efficient.

Figure 1: Substrate scope of scandium catalyzed cycloaddition
of aziridines with different carbonyl heterocummulenes.

Lewis Acid Assisted Ring-Closing Metathesis
Over the past three decades, biodegradable polymers have garnered much attention due to their desirable properties and potential use in medicinal applications. The Nguyen group aims at using ROMP-based biodegradable polymers in their drug delivery system and as such need a method for the synthesis of strained unsaturated medium sized lactones and lactams. Such a methodology for the synthesis of these compounds has been developed and a number of 7-membered lactones can be obtained in good to excellent yield. The methodology requires the coordination of the ester-containing  dienes to a bulky lewis acid (LA). The cavity of the LA then forces the two olefins close together through steric interactions and thereby facilitates intramolecular ring closure while preventing intramolecular ring closure. Work is currently aimed at extending this methodology to include 8-membered lactones and other carbonyl containing substrates.

Scheme 1: Lewis-acid coordination to the carbonyl of the divinyl ester pushed arms of
the substrate "down" to facilitated ring-closing metathesis.

Meerwein-Schmidt-Ponndorf-Verley-Oppenauer
Through mechanistic and kinetic studies, we develop organic methodologies of environmentall- friendly organoaluminum catalysts. We have explored the Meerwein-Schmidt-Ponndorf-Verley-Oppenauer (MSPVO) reduction-oxidation manifold and have extended it to include asymmetric reduction of imines using chiral aluminum compounds. Examples are shown below. Currently, we are developing alkoxyaluminum catalysts that are "greener," safer to handle, more practical and efficient, and more useful for larger scale purposes.

Figure 2: MSPV reduction of imines substrate scope.