Photoisomerisierung von 1,2-Dihydro-1,2-azaborin - eine Matrixisolationsstudie

Accessing 1,2-Substituted Cyclobutanes through 1,2-Azaborine Photoisomerization

We provide a seminal example of the utility of the 1,2-azaborine motif as a 4C+1N+1B synthon in organic synthesis. Specifically, conditions for the practically scalable photoisomerization of 1,2-azaborine in a flow reactor are reported that furnish aminoborylated cyclobutane derivatives. The C-B bonds could also be functionalized to furnish a diverse set of highly substituted cyclobutanes.

The Dewar Isomer of 1,2-Dihydro-1,2-azaborinines: Isolation, Fragmentation, and Energy Storage

The photochemistry of 1,2-dihydro-1,2-azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (>280 nm) with high quantum yield (46 %). Further photolysis with UV light (254 nm) results in the formation of cyclobutadiene and an iminoborane derivative. The thermal electrocyclic ring-opening reaction of the Dewar valence isomer back to the 1,2-dihydro-1-tert-butyldimethylsilyl-2-mesityl-1,2-azaborinine has an activation barrier of (27.0±1.2) kcal mol-1 . In the presence of the Wilkinson catalyst, the ring opening occurs rapidly and exothermically (ΔH=(-48±1) kcal mol-1 ) at room temperature.

1,2-Azaborine: The Boron-Nitrogen Derivative of ortho-Benzyne

The BN analogue of ortho-benzyne, 1,2-azaborine, is generated by flash vacuum pyrolysis, trapped under cryogenic conditions, and studied by direct spectroscopic techniques. The parent BN aryne spontaneously binds N2 and CO2, thus demonstrating its highly reactive nature. The interaction with N2 is photochemically reversible. The CO2 adduct of 1,2-azaborine is a cyclic carbamate which undergoes photocleavage, thus resulting in overall CO2 splitting.