Lithium 2,2,6,6-tetramethylpiperidine LiTMP

Rathice and Kow first reported the preparation of a boron-stabilized carbanion by direct deprotonation of the carbon acid. They made the important observation that the deprotonation needed a sterically demanding base to prevent its complexation with boron. Thus the anion of B-methyl-9-borabicy-clo[3.3.1]nonane, prepared by deprotonation with lithium 2,2,6,6-tetramethylpiperidine (LiTMP) in benzene, can be alkylated successfully. 

Regioselective metalation of a wide variety of trifluoromethylated pyridines and quinolines was exhaustively studied by the Schlosser research group." " It was demonstrated that regioselectivity of direct lithiation of fluorinated heterocycles depends signihcantly on reagents, reaction conditions and type of solvent. For example, the lithiation of 2-CF3-pyridine using lithium 2,2,6,6-tetramethylpiperidine (LiTMP) in THF at —75°C results in exclusive formation of acid 109, while the reaction with BuLi in the presence of Et2NCH2CH20Li in less polar ether leads to selective formation of isomeric acid 110 (Fig. 7.39). ... 

The selection of the lithiation reagent also has a strong influence over the regioselectivity of the electrophilic substitution the bulkier the base, the more favorable the reaction at the C5 position. For example, lithium 2,2,6,6-tetramethylpiperidine (LiTMP) directs the formation of the C5-substituted product at a 79 1 ratio to the C2-substituted thiophene. A variety of electrophiles can be substituted after lithiation by LiTMP. ... 

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