Enantioselective Synthesis of l- and d-Carboranylalanine

Abstract
The enantioselective synthesis of l- and d-carboranylalanine is reported. Imides 13 and 14 are treated with titanium tetrachloride, DIEA, and NBS to introduce a bromo functionality in 98:2 ratio at the α-center. Azide displacement with TMGA, displacement of the oxazolidinone template with titanium tetrabenzyloxide, and subsequent hydrogenolysis permits l- or d-carboranylalanine to be isolated in high stereoselectivity and 35−40% yields overall.