Cyclopentenone Annulation of 1,4-Diketones with Potassium Phosphate Tribasic: A Synthesis of a Monoterpene Alkaloid, (.+-.)-Tecomanine.
作者:Masaaki MIYASHITA、Daisuke TANAKA、Tomonori SHIRATANI、Hiroshi IRIE
DOI:10.1248/cpb.40.1614
日期:——
Conjugate addition of cyclohexanone lithium enolate to 2-nitro-2-butene and the Nef reaction on the resulting nitronate gave 2-(2-oxopropyl)cyclohexanone in good yield. Treatment of the 2-(2-oxopropyl)cyclohexanone thus obtained with potassium phosphate tribasic (K3PO4) in isopropanol gave 2, 3, 4, 5, 6, 7-hexahydro-3-methyl-3aH-inden-2-one (8). Application of the procedure to 1, 3-dimethyl-4-piperidone (11) gave the 1, 3, 4, 6, 7, 7a-hexahydro-6-oxo-2, 4, 7-trimethyl-2H-2-pyrindine (12). Epimerization of 12 with basic alumina gave (±)-tecomanine (1). The short synthesis of the alkaloid demonstrates the usefulness of K3PO4 as a base for cyclopentenone annulation of 1, 4-diketones without migration of the double bond.
将环己酮锂烯酸盐与 2-硝基-2-丁烯进行共轭加成,并对生成的硝酸酯进行奈夫反应,得到 2-(2-氧代丙基)环己酮,收率很高。用异丙醇中的磷酸二氢钾(K3PO4)处理这样得到的 2-(2-氧代丙基)环己酮,得到 2,3,4,5,6,7-六氢-3-甲基-3aH-茚-2-酮(8)。将该步骤应用于 1,3-二甲基-4-哌啶酮(11),可得到 1,3,4,6,7,7a-六氢-6-氧代-2,4,7-三甲基-2H-2-吡啶(12)。用碱性氧化铝对 12 进行二聚化可得到 (±)-tecomanine (1)。这种生物碱的简短合成证明了 K3PO4 作为 1,4-二酮的环戊烯酮环化碱的有用性,而且不会发生双键迁移。