Construction of Boron-Containing Aromatic Heterocycles

Abstract

Boron-containing aromatic systems exhibit unique electronic properties and reactivities that have been extensively studied for a long time. This review highlights the recent developments in the synthesis of aromatic boron-containing heterocycles. The organization of the contents is based on the sizes of rings and the heteroatoms other than boron. Early work in the field is briefly introduced, but the main focus is on recent reports published during the period of 2008 through 2016.1 Introduction2 Five-Membered Rings2.1 Borole Derivatives2.2 B,N-Heterocycles2.3 B,O-Heterocycles3 Six-Membered Rings3.1 Borabenzene Derivatives3.2 Boratabenzene Derivatives3.3 1,4-Diborabenzene3.4 B,N-Heterocycles3.5 B,E-Heterocycles (E = O, S, P, Te)4 Three-Membered Rings4.1 Borirenes4.2 Azadiboriridines4.3 Triboracyclopropenyl Dianion5 Four-Membered Rings5.1 bicyclo-Tetraborane(4)5.2 1,3-Diborete5.3 B,E-Heterocycles (E = N, P, As, Sb, Bi, O, S, Se)6 Seven-Membered Rings (Borepines)7 Conclusion and Perspective

Heavier element-containing aromatics of [4n+2]-electron systems

“…Treatment of the mesoionic carbenes 3-44-3 with P4 also gave 5CP23 and 5CP25 in low yields (Scheme 3-44 B). The each 31 P NMR spectrum of 5CP23-5CP26 shows a doublet at 73 ppm and a triplet at ~325 ppm in 2 : 1 ratio (JP-P = 500 Hz), indicating the presence of an AB2 type system with unsaturated P-P bonds. According to XRD analysis of 5CP23-5CP26, the C2P3 ring is coplanar with the imidazole C3N2 ring.…”

“…In 2021, the Schulz group reported the formation of 2-aza-1,3diphosphaindane-1,3-diyls 5CNP9 and 5CNP10 from reduction of dichloro precursors 3-53-1 (Scheme 3-53). 168 The 31…”

“…26 Aromatic heterocycles involving light elements such as B, N, O, have been extensively studied, and their electronic and chemical properties have been revealed. [27][28][29][30][31] Likewise, the chemistry of aromatic heterocycles containing one or more heavier elements has become a gradually growing field over the past several decades. 7,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] In principle, heteroatoms-containing aromatics, irrespective of light or heavier elements, follow the aromatic concepts for annulenes (Chart 1).…”

“…250 6CP9 was prepared by the reaction of Na(OCP)(diox)2.5 with a chloroborane precursor in THF (Scheme 4-36). The C3P3 ring is characterized by the 31 P NMR resonance at 182.7 ppm and 13 C NMR signal at 226.6 ppm. XRD analysis of light-yellow crystals of 6CP9 shows the planar C3P3 ring with an average C-P bond length of 1.736(4) Å, which is consistent with 6CP8 [1.718(4)-1.729( 5) Å].…”

“…The calculated NICS(1) value of 6CP10 of -8.1 supports its aromatic nature. Subsequent reaction between 6CP10 and tBuPh2SiCl in the presence of 1,8-diazabicycloundec-7-ene (DBU) afforded 6CP11 as indicated by one singlet in the 31 In 2015, the Martin group synthesized 1,2-phosphaborines 6BCP1 and 6BCP2, which were obtained as yellow crystals by irradiation of the benzene solution of pentaarylboroles 4-37-1 and 0.2 equivalents of (PPh)5 over 24 h (Scheme 4-37). 252 The NMR spectra show resonances of the C4BP ring atoms at 77.6 ppm ( 31 P) and 38.4 ppm ( 11 B) in 6BCP1, and 76.9 ppm ( 31 P) and 38.9 ppm ( 11 B) in 6BCP2, respectively.…”