1,2-Azaborine

Benz[e][ 1,2]azaborine, 1,2-dihydro-2-methyl-halogenation, 1, 656 Benz[6]- 1-azafulvenes dimerization, 4, 309 Benz[c]-2-azafulvenes dimerization, 4, 309 Benzazatropolone X-ray analysis, 7, 494 1 -Benzazepine, N-acetyl-6-hydroxy-bromination, 7, 528... 

Ashe has demonstrated that 1,2-azaborines can undergo electrophilic aromatic substitutions [86]. The H NMR chemical shifts of 1,2-azaborines are consistent... 

Hiickel, Pariser-Parr and Pople calculations were applied to 1,2-dihydro-1,2-azaborine (3), 1,2-dihydro-1,2-benzazaborine (14) and 5,6-dihydrodibenz[c,c][l,2]azaborine (15). The calculations were carried out on two models, one with a B—N single bond, the other... 

The instability of 1,2-dihydro-1,2-azaborine towards polymerization does not indicate any substantial stabilization. From this point of view it is surprising to find that some non-fused 2H- 1,2-oxaborines (e.g. 199) seem to be very stable, at least towards heat. The 2,3-dihydro-1,2,3-diazaborine system is the best-known monocyclic system, although the unsubstituted heterocycle has not been prepared so far. It undergoes reactions with certain electrophiles and nucleophiles with maintenance of the unsaturation. 

Owing to their neutron-absorbing properties, some benzo fused 1,2-dihydro-1,2-azaborines have been suggested for use as neutron sensitive material in neutron detectors (67MI12100). 

Thieno[2,3-e][ 1,2]azaborine-6-carboxylic acid, 1,2-dihydro-2-phenyl-3-(2-thienyl)-, methyl ester X-ray, 1, 634 (82UP12100)... 

Diazotization, of 6-amino-2,3-dihydro-1,4-diazepinium salt, 56, 33 Dibenz[c,e][ 1,2]azaborine, 5,6-dihydro-, chlorination, bromination, 59, 309 Dibenz[i/]azepine, and 10,11-dihydro-, lithiation, 56, 273 Dibenziodole( + 1) ions, 56, 338 Dibenzo[fl,c]carbazole, 7-methoxymethyl-, lithiation, 56, 183... 

Benzo[e]-1,2-azaborin 3-Chlor-2-methyl-1,2-dihydro- XIII/3b, 64... 

In a similar approach fV-methyl-3-butenylamine was hydroborated to give 1-methyl-l-aza-2-boracyclohexane. Dehydrogenation gave 1,2-dihydro-1-methyl-1,2-azaborine (112b), an unstable compound whose IR and mass spectra were recorded. In all of these three routes a great deal of polymeric by-products are formed, resulting in very low overall yields. Compound (109 R = Ph) was obtained from (107) in 9.3% overall yield via (108) and in 2% overall yield via (111). 

Yet another approach to a 1,2-dihydro-1,2-azaborine was elaborated by Matteson et al., in which the nitrogen atom was introduced last. The reaction between triborylmethide anions and aldehydes was used to give the four-carbon molecule (126). Treatment of this diborylated ethylene with liquid ammonia caused ring closure to give the pyrimido fused azaborine (127 Scheme 22) (78JOC950). 

Monocyclic 1,2-dihydro-1,2-azaborines (3) easily form polymers with the exception of the 2-phenyl derivative (109 R = Ph), probably because of interaction between the two rings. In contrast, the alkyl substituted monocyclic system (155) is stable towards polymerization although it is easily oxidized by air and hydrolyzed by water. This stability order between (3) and (155) was predicted by semi-empirical methods. However, the ring system (7), isosteric with pyridine, seems to be the most stable of the monocyclic systems. Some of its alkyl derivatives remain unchanged after 50 h in concentrated sulfuric acid at 80 °C. After reflux in IM sodium hydroxide almost all of the compound was recovered. 

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