How Tethers Control the Chemo- and Regioselectivities of Intramolecular Cycloadditions between Aryl-1-aza-2-azoniaallenes and Alkenes

作者：Hong Xin; Liang Yong; Brewer Matthias^*; Houk K N

来源：Organic Letters, 2014, 16(16): 4260-4263.

DOI：10.1021/ol501958s

Cationic 1-aza-2-azoniaallenes react intermolecularly with terminal alkenes to give 1,5-substituted (3 + 2)-cycloadducts, but intramolecular reactions lead to either 1,5- or 1,4-substituted (3 + 2)-cydoadducts or (4 + 2)-cycloadducts, depending on the tether length. DFT calculations and distortion/interaction analyses show that the (CH2)(3) tether prevents the reacting partners from aligning efficiently to give 1,5-substituted (3 + 2)-cydoadducts, and the 1,4-regioselectivity dominates. With the (CH2)2 tether, the (3 + 2) cycloaddition is disfavored due to the forming four-membered ring in the transition state, and the (4 + 2) cycloaddition prevails.

• 出版日期2014-8-15