Asymmetric Lithiation Trapping of N-Boc Heterocycles at Temperatures above -78°C

The asymmetric lithiation trapping of N-Boc heterocycles using s-BuLi/chiral diamines at temperatures up to -20 degrees 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 degrees 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 similar to 90:10 er even at -20 degrees C.