Novel 5-(4-Substituted-phenyldiazenyl)-1,3,2λ⁴-oxazaborines and Their Rearrangement to 1,2,4,3λ⁴-Triazaborines

Abstract

The reaction of substituted benzenediazonium tetraphenylborates with the β-enaminones derived from pentane-2,4-dione, 1-phenylbutane-1,3-dione, and 1,4-diphenylbutane-1,3-dione with a primary or secondary (N-methyl, N-phenyl) amino group in CH2Cl2 gives 5-(substituted-phenyldiazenyl)-2,2-diphenyl-4,6-disubstituted-1,3,2λ4-oxazaborines or 5-(substituted-phenyldiazenyl)-2,2-diphenyl-3,4,6-trisubstituted-1,3,2λ4-oxazaborines, respectively. The reaction intermediate of these compounds has been identified, and a mechanism for the reaction has been suggested. Substituted 1,3,2λ4-oxazaborines gradually rearrange into 1,2,4,3λ4-triazaborines at temperatures above 100 °C.

Straightforward access to oxazaborines, diazaborinones and triazaborines by reactions of β-enaminoamides with 4-methylbenzenediazonium tetraphenylborate

“…The chemical shift of boron atom in the compound 4a (d( 11 B) = À1.46 ppm ( Table 2)) is comparable with the measured values for the earlier-studied triazaborines [22] prepared from benaminones. Scheme 2 suggests two possible structures for triazaborines, namely B and C. Fig.…”

“…When suggesting the structure of compounds 2a, 3a, 4a, we started from the previously described mechanism of the reaction of b-enaminones with diazonium tetraphenylborates [22]: the primary product of the azo coupling reaction reacts with tetraphenylborate anion with gradual splitting off of two molecules of benzene and ring closure giving the heterocycle. The primary product of the azo coupling reaction can exist in several forms stabilised by the formation of intramolecular hydrogen bonds.…”

“…Hence, by increasing temperature it is possible to obtain diazaborinone also from b-enaminoamides having a secondary enamino group. The difference in thermal rearrangement of oxazaborines 2a-d as compared with the oxazaborines prepared from b-enaminones [22] lies in the fact that compounds 2c and 2d (derived from enamioamides with N-methyl group) give triazaborines already at room temperature or at enhanced temperature, while the oxazaborines with N-methyl group derived from b-enaminones [22] either do not undergo thermal rearangement at all or undergo it but very unwillingly, the yields of triazaborines being poor.…”

“…Recently we published a new method of preparation of substituted 1,3,2k 4 -oxazaborines by reaction of the corresponding b-enaminones with 4-substituted benzenediazonium tetraphenylborates in dichloromethane at room temperature [22]. We also suggested a mechanism of formation of oxazaborines.…”

“…We also suggested a mechanism of formation of oxazaborines. Thermal rearrangement of the mentioned oxazaborines leads to substituted 4H-1,2,4,3k 4 -triazaborines [22].…”