Syntheses of heterocyclic compounds. CCCXCV. Synthesis of homopetaline-type compounds

Abstract

extracted with ether. The extract was washed with sodium chloride solution, dried over K2C03, and distilled off to give 330 mg of a stereoisomeric mixture of amino ester 12 [ir (CHC13) 3450, 2900, 2750, 1720, and 1600 cm"1; m/e 300 (M+)], which was used in the following reaction without purification because of difficult crystallization.(±)-Isodasycarpidone ( 15) and (±)-Iso-5-epidasycarpidone (16).-A mixture of 300 mg of the amino esters 12,1 g of potassium hydroxide, 10 ml of water, and 20 ml of ethanol was refluxed for 5 hr. The resulting mixture was neutralized with concentrated hydrochloric acid and the solvent was evaporated completely to give a residue, which was extracted with dry ethanol.Removal of the extract gave 270 mg of 5-ethyl-4-hydroxycarbonyl-2-(3-indolyl)-l-methylpiperidine (14) as a powder, which was treated with polyphosphoric acid (prepared from 2 ml of phosphoric acid and 4 g of phosphorus pentoxide) at 90-95°for 1 hr. To the reaction mixture was added 5 ml of water, and the resulting mixture was basified with ammonia and extracted with ether. The extract was washed with sodium chloride solution, dried over K2C03, and distilled off to give 98 mg of a pale yellow syrup, whose preparative thick layer chromatography (ethyl acetate-benzene-methanol, 2:2:1) on silica gel afforded 16 mg of (± )-isodasyca,rpdione (15) and 9 mg of (± )-iso-3-epidasyc arpidone ( 16). Recrystallization of 15 from methanol-ether gave colorless needles: mp 220-221°; ir (CHCls) 3430, 2900, 2780, and 1645 cm-1; nmr