Functionalized isoquinolines react with triallylborane to produce 1,3-diallylated 1,2,3,4-tetrahydroisoquinolines 1-8 with excellent chemo- and stereoselectivity. In these conditions 4-bromoisoquinoline was converted into tricyclic aziridine 10. Synthesis of monoallylated tetrahydroisoquinolines using allyldipropylborane and reduction with NaBH4was also developed. © 2002 Elsevier Science B.V. All rights reserved.