Design and evaluation of a new Lewis acid-assisted Lewis acid catalyst system and further applications of a double-allylation reagent

Abstract

Asymmetric synthesis is one of the most important areas of organic chemistry. Despite of the prevalence of asymmetric catalysts, there is still room for improved catalyst systems. Chapter 2 describes the design and evaluation of a new Lewis acid-assisted Lewis acid (LLA) catalyst system. Many boronic esters were prepared for this purpose and combined with different Lewis acids to form LLA catalyst systems. These LLA species were examined in carbonyl allylation reactions. In a few cases, higher product conversions were observed with the new LLA catalyst systems compared to the corresponding background reactions (Lewis acid alone). A novel class of chiral double-allylation reagent 7 was recently introduced by our group. Hall and Peng showed the stereoselective synthesis of trisubstituted furans, vinylcyclopropanes, and smaller oxabicyclic compounds using this double allylation reagent. Chapter 3 describes further applications of double allylation reagent 7. In this chapter, the synthesis of larger oxabicyclic compounds, a one-pot synthesis of furan rings, and the synthesis of pyrrolidines were examined. From the preliminary studies, it was observed that the synthesis of pyrrolidines may be feasible. Moreover, trisubstituted tetrahydrofurans 46_49 were prepared in a one-pot protocol with excellent diastereoselectivities (≥20:1).