2-(2-Oxocycloalkyl)- or 2-phenylacyl-3-tosyl-1,3-oxazolidines 1, 2, 9, and 10 undergo with 3-buten-2-one highly diastereoselective Michael additions under the influence of cesium carbonate to yield 1,5-diketones 8 or 11, respectively. Intramolecular aldolization of diketones 8 yields stereohomogeneous cyclohexanones 13 or 14. Addition of nucleophiles to ketones 14, again, proceeds highly stereoselectively to give diols 17. Overall, under the stereodirecting influence of N-tosyl-2-aminoalkanols, stereohomogeneous protected carbaldehydes are constructed within a few steps from simple achiral precursors.
在
碳酸铯的影响下,2-(2-氧代环烷基)- 或 2-
苯乙酰基-3-对
甲苯磺酰基-
1,3-恶唑烷 1、2、9 和 10 与 3-
丁烯-2-酮发生高度非对映选择性的迈克尔加成反应,分别生成 1,5-二酮 8 或 11。二酮 8 的分子内醛化反应生成立体同构的
环己酮 13 或 14。酮 14 与亲核物的加成同样具有高度的立体选择性,可得到二元醇 17。 总之,在 N-对甲基苯磺酰-2-
氨基烷醇的立体定向影响下,只需几个步骤就能从简单的非手性前体中生成立体同构的受保护羧醛。