DIASTEREOSELECTIVE RADICAL REACTIONS STARTING FROM CYCLIC IODOHYDRIN DERIVATIVES

The stereoselectivity of radical reactions using cyclic iodohydrins and 2-alkoxy iodides was investigated on a simple model system obtained from indene (see 1a-d). The low level of stereoselectivity inherent to this type of systems could neither be overcome by using large protective group on the O-atom of Ic nor by complexation with Lewis acids. However, starting from the free alcohol Ic, it was possible to obtain very high selectivities (trans/cis > 100:1) by forming an aluminium alkoxide derivative upon treatment with methylaluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) before running the radical reaction. Despite the high steric demand of these complexes, the reactions gave satisfactory yields even for the formation of C-C bonds.