1 Lewis Acid – Brønsted Base Catalysis

From the synthetic point of view, organic synthesis via catalytic processes offers many benefits. Catalysis frequently obviates the excessive use of the activating reagents and associated tedious purification processes, thereby offering more environmentally benign synthetic processes. Furthermore, the specific activation mode of a catalyst allows for highly chemoselective transformations that are seldom achieved by noncatalytic processes. Over the past two decades, the concept of cooperative catalysts has evolved and subsequently rapidly advanced as the most finely refined class of artificial catalysts for preparative chemistry [1]. The cooperative catalysts exhibit two catalytic functions simultaneously to achieve a dual activation mode to specific substrate(s) (Figure 1.1). The obvious advantage of this activation strategy is not only the significant enhancement of the reaction rate due to intramolecularity or a proximity effect but also the broadened scope of the applicable reactions following the synergistic activation of otherwise unreactive substrate sets. In this chapter, cooperative catalysts that exhibit Lewis acid and Brønsted base activation modes are reviewed. While recent interest in artificial catalysts focuses on the efficient production of enantioenriched building blocks [2], herein only asymmetric Lewis acid–Brønsted base cooperative catalysts are covered. Metalbased asymmetric cooperative catalysts that display transition-metal catalysis are described in other chapters [3]. In this chapter, the focus is on the reactions promoted by the effective coupling of an in situ generated active nucleophile by a Brønsted base and an electrophile activated by a Lewis acid.