Preparation of Chiral Allenylmetal Reagents from Enantioenriched Allenyl Iodides and Propargylic Mesylates. A Comparison of Indium, Bismuth, and Tin Derivatives

Chiral allenylmetal halides were prepared starting from enantioenriched (∼95% ee) 1-octyn-3-ol mesylate (1) and 3-butyn-2-ol mesylate (7). Addition of these transient metallo species to aldehydes in situ afforded mainly anti homopropargylic alcohol adducts of varying ee. Three approaches were explored. In the first, the mesylates were converted to allenylstannanes with Bu3SnLi·CuBr and the allenylmetal halide was prepared from the resulting enantioenriched allenylstannane by transmetalation with InBr3, BiBr3, and SnCl4 in the presence of cyclohexanecarboxaldehyde. The configurational stability of the transient allenylmetal halide was estimated from the ee of the derived adduct. The second approach involved metalation of the allenyl iodides prepared from mesylates 7 and 1 through SN2‘ displacement with LiCuI2. From these experiments, it was determined that allenylindium bromides and allenyltin bromides are configurationally stable under the reaction conditions. The adduct obtained from the allenylbismuth b...