Regio- and diastereoselective formation of some (η6-2-methylindoline)tricarbonylchromium(0) complex derivatives

Complexation of 2-methylindoline 1 and its derivatives 2 and 3 with Cr(CO)6 gave complexes 4–9. With the TIPS group attached to the nitrogen atom as in compound 3, the complexation was completely diastereoselective producing the endo complex 9. Treatment of the metallated complexes 8 and 9 with 2-halobenzoyl chlorides as electrophiles allowed for totally regioselective functionalisation at C(4), while the exo complex 6 was functionalised both at C(4) and C(7); with TMSCl and TIPSCl as electrophiles, the endo complex 9 also exhibited minor exo benzylic substitution to give 25 and 27. Oxidative decomplexation of the indoline complexes efficiently releases the free 4-substituted indolines.