Conjugate addition reaction of THF-2-yl radical with α,β-unsaturated N-tosyl imines using a dimethylzinc-air initiator

The reaction of tetrahydrofuran-2-yl radical, generated directly from THF by the action of dimethylzinc-air, with α,β-unsaturated N-tosyl aldimines was demonstrated to proceed preferentially in a conjugate addition manner to give 2-(3-hydroxyalkyl)- or 2-(3-aminoalkyl)tetrahydrofurans in good yield. The slow addition of the enimines and the use of dimethylzinc, rather than diethylzinc or triethylborane, were found to be the keys for the efficiency of the THF conjugate addition. The observed chemoselectivity could be rationalized by the larger coefficient of LUMO at the corresponding reaction site of the enimine.