Enantioselective [4 + 2]-Annulation of Chiral Crotylsilanes:  Application to the Synthesis of a C1−C22 Fragment of Leucascandrolide A

The asymmetric synthesis of a C1−C22 fragment (2) of leucascandrolide A is described. Synthetic highlights include the construction of the C9−C22 pyran fragment using a formal [4 + 2]-annulation of a chiral organosilane. A diastereoselctive Mukaiyama aldol was used to introduce the C9 stereocenter and complete the assembly of the macrocycle's carbon skeleton.