Halocyclization by a ‘Chiral Iodine Atom’

Significance

A method for the enantioselective halocyclization of homo(polyprenyl)arenes (1a-d) induced by chiral phosphoramidite 4 as nucleophilic promoter has been developed. As shown by the authors, various simple P-nucleophiles can also be used catalytically (30 mol%) in a non-asymmetric variant of the described transformation. However, enantiomeric excess is only achieved by using the chiral phosphoramidite in stoichiometric amount. The use of NBS instead of NIS results in both decreased yield and decreased enantioselectivity. Furthermore, the strong solvent effect (no chiral induction in CH₂Cl₂) is discussed and a reaction mechanism to rationalize the observed stereo­chemical outcome is proposed.