Aniline is a poor guide to lithium: lone pair electrons of 195 n are less basic than amines, and nitrogen is less acidic than corresponding oxygen substituents. In reflow hexane,N, N-dimethylaniline can still be lithium by BuLi, and the lithium efficiency of N, N-dialkyl aniline is higher after TMEDA is added.
So far, the best solution to the problem of amino-substituted aryl ring lithium is to acylation of aniline to neopentaniline or N-boc carbamate. Two equivalent bases (BuLi) first deprotonate the nitrogen and then completely prolize the anion to produce it. As with the secondary amides described above, the lack of acidification in the anionic intermediate (at this time cyclic conjugated) outweighs the strong lithium coordination capacity of the anionic intermediate.
For N-Boc aniline, the best condition for lithium is t-Buli (2.2 equivalent) in Et2O at -10 °C.
Amides of aminopyridine are also widely used to guide lithium and are most effective when lithium with BuLi in the absence of TMEDA. The lithium of 218 can be used as a key step in the synthesis of naphthalene and other thickened polycyclic heterocycles.
N-lithium of thioaniline 219 has been used to construct benzothiazole ring 221 from benzylene 220.
Urea of aniline 222 can also be lithium. The product is usually difficult to crack, but carbon monoxide quenching of the intermediate organic lithium 223 results in the formation of acyllithium 224, which is cyclized to form indired 225.
The choice of oil for a given polymer depends on the presence of polar groups in the polymer, such as the -CN group in NBR and the -Cl group in CR. Hydrogen bonding and van der Waals forces affect the availability of oils in compounds. Table 9.29 gives a general guide for selecting an oil for a given polymer. This selection guide must be brief and have many exceptions. Key parameters to be noted are the tendency of oil to discolor the product, the tendency of oil to contaminate adjacent components in the product, and the solubility of oil in the polymer (Barbin and Rodgers, 1994).
