Indolylzinc reagent

Bosch s group cross-coupled both 2- and 3-indolylzinc derivatives with diversely substituted 2-halopyridines to assemble 2- and 3-(2-pyridyl)indoles, which have become important intermediates in indole alkaloid synthesis [23-28]. Thus, l-(phenylsulfonyl)indole (30) was converted to 2-indolylzinc reagent 32, which was then coupled with 2-halopyridine 33 to secure 2-(2-pyridyl)indole 34. 

Recognizing that l-(phenylsulfonyl)-3-lithioindole tends to isomerize to the corresponding 2-lithioindole derivative, Bosch et al. used a silyl ether protection to solve the problem. They prepared 3-indolylzinc reagent 36 from 3-bromo-l-(terr-butyldimethylsilyI)indole (35) and then coupled 36 with 2-halopyridine 33 to form 3-(2-pyridyl)indole 37. Finally, the Negishi adduct 37 was further manipulated to a naturally occurring indole alkaloid, ( )-nordasycarpidone (38) [23,27]. 

---