Synthesis of (+)-(R)-1-Amino-2,2-difluorocyclopropane-1-carboxylic Acid through LipaseCatalyzed Asymmetric Acetylation

A cyclic tetramer of optically active spirosilane 1 was prepared as a new chiral molecular square with D4 symmetry by the Pd-catalyzed cross-coupling reaction, which shows a larger anisotropy factor g in the CD spectrum relative to a series of linear oligomers of 1.