Final answer:
Lithiation at the C4 position with t-BuLi, rather than the C2 position, is likely due to steric and electronic factors influencing the reactivity and acidity of the positions on the substrate. This selectivity is a common feature in organic synthesis, allowing for targeted functionalization of molecules.
Step-by-step explanation:
The specific lithiation at the C4 position with t-BuLi rather than the C2 position may be influenced by several factors, including steric hindrance and electronic effects. Generally, t-BuLi is bulky, and thus tends to deprotonate less hindered positions. Moreover, surrounding substituents' electronic properties can make certain positions more acidic and, therefore, more susceptible to deprotonation. For example, an electron-withdrawing group at the C2 position may lower the acidity and reduce the rate of deprotonation at that site by t-BuLi. Conversely, electron-donating groups or lesser steric hindrance at the C4 position would increase the rate of lithiation at that position.
Lithiation reactions are selective, and this selectivity is often exploited in organic synthesis to functionalize molecules at specific positions. If steric or electronic factors favor the C4 position, t-BuLi will most likely deprotonate there, leading to selective C4-lithiation. While the exact reason behind the selectivity in a particular reaction would need to be analyzed with regards to the substrate's structure, these general principles often guide the deprotonation patterns.
The preference for C4-lithiation over C2 with t-BuLi in certain substrates from the Baran group meeting material could be due to these principles and is likely explained in more detail in their experimental observations and mechanistic studies.