We then turned our attention to further assessing the most promising catalysts 14 in cross-aldol reactions of a variety of ketones with p-nitrobenzaldehyde (Table 2). Proline-catalysis was effective for 2-butanone affording aldol adducts 3 and 4 in good yield with modest regio- and diastereoselectivity (Entry 1) but provided 5 with no diastereoselectivity when cyclohexanone was used as the donor ketone (Entry 2). Furthermore, 3-pentanone was not a donor under L-proline catalysis but ...
