Novel Synthesis of Alkenes via Triethylborane-Induced Free-Radical Reactions of Alkyl Iodides and β-Nitrostyrenes
journal contributionposted on 2001-08-15, 00:00 authored by Ju-Tsung Liu, Yeong-Jiunn Jang, Yuh-Kuo Shih, Shin-Ru Hu, Cheng-Ming Chu, Ching-Fa Yao
Reactions of (E)-β-nitrostyrenes 1 and triethylborane 2 or tricyclohexylborane 4 in THF solution at room temperature in the presence of oxygen in the air as radical initiator generate high yields of trans-alkenes (E)-3 or (E)-5. Medium to high yields of different (E)-alkenes (E)-5, 7, 10, 12, and 14 also can be prepared when 1 reacts with different radicals, prepared from secondary alkyl iodides 6 and 8 or tertiary alkyl iodides 9, 11, and 13, in the presence of 2 and air as radical initiator. The generation of the only product (E)-alkenes can be explained by the generation of the benzylic radical A and/or B as the intermediate only and the mechanism is similar to Scheme . Both (E)- and (Z)-16a−c are generated when (E)- and (Z)-15a−c are used to react with adamantyl radical under similar conditions. Only (Z)-16d was observed when either (E)- or (Z)-15d was used to react with adamantyl radical. The generation of the (E)- and/or (Z)-alkenes can be explained by the free rotation of the A and/or B to generate A‘ and/or B‘ and vice versa, and the mechanism is proposed to be a free-radical reaction via NO2/alkyl substitution and is shown as Scheme .