Cyclopentenone annulation of 1,4-diketones with potassium phosphate tribasic: A synthesis of a monoterpene alkaloid, (±)-tecomanine

Article abstract of DOI:10.1248/cpb.40.1614

Conjugate addition of cyclobexanone 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.

Full text of DOI:10.1248/cpb.40.1614

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