4
S.C. Pan, B. List
Sauer–Wiechert reaction (Eder et al. 1971; Hajos and Parrish 1974;
for a review, see List 2002b; Scheme 2), an intramolecular aldol reaction catalyzed by proline. Despite its use in natural product and steroid
synthesis, the scope of the Hajos–Parrish–Eder–Sauer–Wiechert reaction had not been explored, its mechanism was poorly understood, and
its use was limited to a narrow context. Inspired by the development
of elegant biocatalytic and transition metal complex-catalyzed direct
asymmetric aldolizations (Barbas et al. 1997; Yamada et al. 1997), a revival of this chemistry was initiated with the discovery of the prolinecatalyzed direct asymmetric intermolecular aldol reaction about 30 years
later (List et al. 2000; also see Notz and List 2000). Since then, prolinecatalyzed enantioselective intermolecular aldol reactions (Northrup and
MacMillan 2002a; Bøgevig et al. 2002a; Chowdari et al. 2002; Córdova
et al. 2002a,b; Sekiguchi et al. 2003; Bøgevig et al. 2003), Mannich reactions (List 2000; List et al. 2002; Hayashi et al. 2003a; Córdova et al.
2002c; Hayashi et al. 2003b; Córdova 2003; Notz et al. 2003; Enders
et al. 2005; Ibrahem et al. 2004) and Michael additions (List et al. 2001;
Enders and Seki 2002) have been developed (List 2004; Allemann et al.
2004).
Scheme 1. Organocatalytic cycles