Non-bonding 1,5-S•••O interactions govern chemo- and enantioselectivity in isothiourea-catalyzed annulations of benzazoles
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Isothiourea-catalyzed annulations between 2-acyl benzazoles and α,β-unsaturated acyl ammonium intermediates are selectively tuned to form either lactam or lactone heterocycles in good yields (up to 95%) and high ee (up to 99%) using benzothiazole or benzoxazole derivatives, respectively. Computation gives insight into the significant role of two 1,5-S•••O interactions in controlling the structural preorganization and chemoselectivity observed within the lactam synthesis with benzothiazoles as nucleophiles. When using benzazoles the absence of a second stabilizing non-bonding 1,5-S•••O interaction leads to a dominant CH•••O interaction in determining structural preorganization and lactone formation.
Robinson , E R T , Walden , D M , Fallan , C , Greenhalgh , M D , Cheong , P H-Y & Smith , A D 2016 , ' Non-bonding 1,5-S•••O interactions govern chemo- and enantioselectivity in isothiourea-catalyzed annulations of benzazoles ' , Chemical Science , vol. 7 , no. 12 , pp. 6919-6927 . https://doi.org/10.1039/C6SC00940A
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