The asymmetric lithiation trapping of N-Boc heterocycles using s-BuLi/chiral diamines at temperatures up to −20 °C is reported. Depending on the N-Boc heterocycle, lithiation is accomplished using s-BuLi and (−)-sparteine or the (+)-sparteine surrogate in the temperature range −50 to −20 °C for short reaction times (2–20 min). Subsequent electrophilic trapping or transmetalation–Negishi coupling delivered functionalized N-Boc heterocycles in 47–95% yield and 77:23–93:7 er. With N-Boc pyrrolidine, trapped products can be generated in ∼90:10 er even at −20 °C.
Gelardi, G., Barker, G., O'Brien, P., & Blakemore, D. C. (2013). Asymmetric Lithiation Trapping of N-Boc Heterocycles at Temperatures above −78 °C. Organic Letters, 15(21), 5424-5427. https://doi.org/10.1021/ol402395j