Total synthesis of quinolizidine alkaloids(-)-lasubine II

Aim:To study and improve enantioselective total synthesis of quinolizidine alkaloid(-)-lasubine Ⅱ.Methods:A new approach to total synthesis of (-)-lasubine Ⅱ was established from readily available starting materials,via the new synthetic sequence including the creation of stereogenic centers through two sequential highly stereoselective Roush allylborations,SN2 cyclization and ring-closing metathesis reactions for the construction of the lasubine′s quinolizidine skeleton.Results and Conclusion: The synthesis of natural product(-)-lasubine Ⅱ has been accomplished by a new synthetic route in an overall yield of 15.3% and its spectrum data,including 1H NMR,13C NMR,EI-MS,IR and optical rotation,is in agreement with the literature data.