BN‐Butafulvenes and Their Application in the Synthesis of Highly Substituted BN‐9,1‐Naphthalenes

Abstract

AbstractBN‐butafulvenes, mono‐BN isosteres of butafulvene and highly strained isomers of azaborines and B‐amino boroles, have been synthesized via hydrolysis of the urana‐borabicyclic complexes obtained from the reactions of bis(alkynyl)boranes with an uranacyclopropene complex. Their 4‐dimethylaminopyridine (DMAP) adducts can further isomerize to 1,2,4,6‐multisubstituted BN‐9,1‐naphthalenes. Both NMR reaction monitoring and theoretical calculations point to a reaction mechanism involving dearomative insertion of DMAP followed by two consecutive 1,2‐hydrogen shifts. The photophysical studies of the highly substituted BN‐9,1‐naphthalenes reveal a notable redshift in both the UV/Vis absorption and emission spectra. The (TD)‐DFT calculations corroborate the experimental data, suggesting that the strong π‐donating amino substitution at the 1‐ and/or 6‐positions destabilizes the HOMO, and thus leading to a notable decrease of the HOMO–LUMO gap.