Synthesis of tetrahydrobenzoisoquinolinols, tetrahydropyrindines, and hexahydroquinolines from 4-aryltetrahydropyridines

A straightforward synthesis of tetrahydrobenzoisoquinolinols 2, tetrahydropyrindines 3, and hexahydroquinolines 4 from versatile intermediate 6 is reported. Two key transformations were carried out by intramolecular Friedel–Crafts cyclization and ring-closing metathesis in moderate yields. Skeleton 6 was easily prepared from the known starting material 4-aryl-4-methoxypiperidin-3-ones 7 via Wittig olefination with Ph3P=CHCO2Et, deconjugation with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and boron trifluoride etherate (BF3–OEt2)-catalyzed addition of the corresponding iminium ion with allyltrimethylsilane.