Synthesis of Functionalised Indoline and Isoquinoline Derivatives through a Silylcarbocyclisation/Desilylation Sequence

A two steps sequence of silylcarbocyclisation-TBAF promoted desilylation/aryl migration has been applied to the synthesis of indolines and tetrahydroisoquinolines derivatives starting from suitable tosylamides and aryldimethylsilanes. In both cases silylcarbocyclisation reactions determined the formation of the heterocyclic ring together with the insertion of a CO functionality. Under the experimental conditions the carbonyl moiety is reduced to OH quantitatively. Subsequent treatment of silylated indolinols with TBAF generates stereoselectively the corresponding arylmethyl-tosylindolinols. In the case of tetrahydroisoquinolinols, during the desilylation step, migration of the aryl moiety is followed by spontaneous loss of water thus affording 3,4-dihydroisoquinolines exclusively.