First synthesized in 1963 by van Tamelen, Dewar benzene consists of two fused strained cyclobutenes. Suitably substituted derivatives are promising as energy storage materials due to the reversibility of the Dewar benzene formation. For example, hexafluorobenzene is selectively and in high yield photoisomerized to its high energy Dewar isomer, whereas the Dewar isomer of hexamethylbenzene is sufficiently stable to release thermal energy only on demand (Figure ). Dewar benzene derivatives have also been utilized in holographic 3D-information storage, taking advantage of quantum-amplification effects of the photoisomerization, and they have been embedded into polymers to achieve new reconfigurable materials that undergo main-chain structural transformations via valence isomerization. The materials discussed above consist solely of carbon atoms in their backbone, and heteroaromatic analogs of Dewar benzene remain exceedingly rare. Heteroarenes with B-N units embedded in the aromatic framework provoke ever increasing interest due to the extensive applications that are emerging in biochemistry and pharmacology, materials science, and catalysis. The isosteric replacement of C=C for B-N units in benzene to furnish 1,2-azaborinines has proved to be a particularly effective approach. Importantly, azaborinines exhibit significant differences in the aromatic delocalization from benzene. As a consequence, they present distinct reactivity at different ring positions that allows for selective functionalization. In a remarkable recent development, Bettinger and Liu discovered that 1,2-dihydro-1-tert-butyldimethylsilyl-2-mesityl-1,2-azaborinine (A) undergoes photoconversion into the corresponding Dewar valence isomer (B) upon irradiation with UV light (> 280 nm) (Figure ). The kinetically stable isomer B can be converted back to A by a thermal electrocyclic ring-opening reaction that requires an activation energy of (27.0 ± 1.2) kcal mol -1 (half-life of 25 min at 100 ºC). In the presence of Wilkinson's catalyst, the ring-opening occurs rapidly and exothermically even at room temperature. Pursuing new synthetic pathways that take advantage of the facile formation of highly functional BN-Dewar benzene derivatives, Liu and coworkers also developed a strategy to 1,2-substituted cyclobutane derivatives via hydrogenation and subsequent ring-opening of the 4-membered B-N heterocycle. Inspired by these results, we hypothesized that the presence of a strained cyclobutene ring system in BN Dewar