Quaternary Phosphonium Salt-Catalyzed Mannich Reactions

3 Quaternary Phosphonium Salt-Catalyzed Mannich Reactions 

Phase-transfer catalysis is critical not only to industrial manufacturing of high-performance chemical products in low-cost processes but also to academic research on various asymmetric bond formation reactions under mild conditions. The beneficial properties of phase-transfer catalysis such as simple operation, rruld conditions, inexpensive reagents and solvents, and large-quantity preparations could open the way to a seamless development of synthetic methods from academia to industry [93]. 

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Scheme 28.26 Quaternary phosphonium salt-catalyzed Mannich reactions.

The construction of a quaternary chiral center in 3-aryloxindoles 209 is of interest, since this structure is present in several biologically and pharmaceutically active compounds. Newly designed phosphonium salt 208 catalyzes the Mannich reaction between 3-aryloxindoles (206) and activated imines (207) in quantitative yields with excellent diastereoselectivity and high enantioselectivity under phase-transfer conditions (Scheme 28.26) [105]. 

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