Synthesis and Absolute Configurations of Halogenoallenes

The highly stereoselective synthesis of 3-methyl-1-halogenoallenes, 3-tert-butyl-1-halogenoallenes, and 1,3-ditert-butylallene is described. The R absolute configuration is assigned to the levorotatory halogenoallenes by relating them to allenes of known configurations. The configurational assignments are in agreement with (vacuum) circular dichroism data for the tert-butylallenes. The obtained results are used to clarify the hitherto existing confusion in the literature concerning absolute configurations of chloro and bromoallenes. Further, the signs and magnitudes of the ligand specific parameters for the halogens in the chirality functions approach, used to predict optical rotations of allenes, are discussed. The literature parameter for chlorine is revised and adequate numerical values for those of bromine and iodine are proposed.