Pyrrolizinone‐Fused BOPYINs: Characterization and Selective C‐O Bond Formation Mechanism.

Two novel pyrrolizinone‐fused BOPYINs (DAB−M and DAB−U) were prepared in one‐step through the oxidative and/or oxidative nucleophilic substitution of hydrogen (ONSH) reaction. Selective methoxyl substitution of α‐unsubstituted BOPYIN was developed, in which C−O and C=O bonds were formed and demonstrated by the single crystal structure of DAB−M. The absorption and emission spectra of both compounds showed red shift and large Stokes Shift compared with starting material DAB. Based on the TD‐DFT calculation, the electron transfer direction is totally different from DAB due to the carbonyl group on pyrrolizinone unit. Besides, a reasonable mechanism has been proposed and evidenced by quantum calculation in which the relative free energy has been exhibited. [ABSTRACT FROM AUTHOR]