DFT Study On The Mechanism Of Synthesizing Bicyclic Furo[3,2-c] Pyridinones And N-sulfonyl Amidine

Reducing the cost of synthesizing organic compounds is the significant aim forthe chemists. In2011, Liang’s group reported a novel strategy for synthesizingbicyclic furo[3,2-c]pyridinones. Unlike other reports in the past, this reaction realizesthe Anion Relay Chemistry via non-Brook rearrangement. In2013, Liang’s groupreported a new tactic to synthesize N-sulfonyl amidine using hydrogen bond, whichbroadened the hydrogen bond catalyzing field. However, the mechanisms of thesereactions and how do the experimental conditions influence the mechanisms are stillunclear, we decide to use DFT method to investigate them. Our work include into twoparts:We investigate the mechanism of synthesizing bicyclic furo[3,2-c]pyridinones atthe B3LYP/6-31+G(d,p)-D//B3LYP/6-31G(d) level. The reaction can be classifiedinto three steps: Aza-Michael addition, ring opening and recyclization, electrophiletrapping. The results show that: In the first step, NaH initially extracts the proton ofthe imine, causing the aza-Michael addition, and this corresponds to the “throughbonds” negative charge transfer. The second step, ring opening and recyclization,corresponds to the “through space” negative charge transfer, and has the highestenergy barrier meaning this is the rate-determine step. We take the Natural BondOrbital (NBO) analysis of the relevant species, finding that negative charge transfersfrom N to O to C. By analyzing the LUMO of the key transition state, we find thatduring the ring opening step, the empty orbital of Na+makes the orbital coverbetween the P orbital of the Carbon and the P orbital of the Oxygen become possible,which is necessary for the ring opening process. We find that this is the first case thatAnion Relay Chemistry is realized via Non-Brook rearrangement involving both“through bonds” and “through space” negative charge transfer, and this provides theoretical foundation for this kind of reactions.We also investigate the mechanism of synthesizing N-sulfonyl amidine atB3LYP/6-31G(d) level. Under the hydrogen Bond’s assistance without or with NBS,N-sulfonyl amidine can be obtained from benzenesulfonamide and formamide. Theresults show that: with the assistance of hydrogen bond, the proton transfer takesplace, and the reaction happens. When adding NBS, the Br atom replaces one protonfrom the imine, changing the charge distribution. This further reduces the energybarrier, and makes the reaction more reactive. This mechanism offers a new methodfor synthesizing N-sulfonyl amidine catalyzed by hydrogen bond.