Pd-Catalyzed Ligand-Directed Divergent Cycloaddition of Cyclic 1-Azadienes with Oxo-1,4-dipoles
Hongling Xie, Lei Chen, Zhengyu Han, Zhenkun Yang, Jianwei Sun, Hai Huang
Abstract
Ligand-directed divergent synthesis (LDS) is an important synthetic tool for the preparation of structurally diverse organic molecules without tedious steps to modify substrates. Herein, we introduce the realization of 3,4-, 1,2-, and 1,4-cyclization of benzo[ d ]isothiazole-1,1-dioxide-fused azadienes (BDAs) through LDS, leading to tetrahydro-2 H -pyrans, oxazinanes, and tetrahydro-2 H -1,5-oxazocines, respectively. Using phosphinooxazoline (PHOX) ligands, we have developed a [4 + 2] cycloaddition between BDAs and substituted 2-alkylidenetrimethylene carbonates, providing access to multi-substituted chiral tetrahydro-2 H -pyrans in good yields with excellent enantio-, diastereo-, and regioselectivities.