However, treating 2-lithiothiophene with quinoline at 20Β°C by Giiman's methodf6] leads only to 2-(2-thienyl)quinoline (2) (38%), indicating steric hindrance of 4-addition by the peri-hydrogen atom of the quinoline. In the following reactions of the quinoline system with 2-lithiothiophene derivatives substitution is also only at the 2-position. a-% ' R e cxpqwa S (4)
QcJUa-0 s s
The yield of 2-(2-thienyl)quinoline (2) could be raised to 75% by causing the components to react at 45Β°C [2 h in ether/n-hexane (2: I)], the 2-position of the thienyl group being provided by an analogous synthesis from 2-chloroquinoline instead of quinoline and by NMR spectroscopy. The lithium compoundc6] obtained therefrom by n-butyllithium [yield 33% on the basis of the yield of alcohol (m. p. 221 "C) resulting from treatment with benzophenone] reacts with quinoline to give the trisarene ( 3 ) and with CuCl, to give the tetrakisarene (4). As shown in the formula scheme and Table, compound (4) was accessible in higher yield by reaction of 2,2'-bithiophene and 2 mol of n-butyllithium with subsequent treatment with quinoline. The analogous reaction with one mol of the two reagents gave the trisarene (6) as main product. lithium in ether/n-hexane (9 : 1) only in the thiophene rings and not on the aliphatic bridge. The yield of (8) is considerably better than that of ( 9 ) since the monolithium derivative from (7) is in equilibrium with the dilithium compound and the unmetalated compound.
The Table records the reaction conditions, yields, and properties of the apparently new compounds prepared, their structures being proved by elemental analyses, mass and NMR spectra, and the method of their preparation.