Heterocyclic organoboron compounds—XVI

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

“…It is known that substituted 1,3,2λ 4 -oxazaborines are formed by the reaction of β-enaminones with diphenylborinic acid or its derivatives. The question of whether in our case the first process is formation of 3,4-dimethyl-2,2,6-triphenyl-1,3,2λ 4 -oxazaborine ( 16 ) from 3-(methylamino)-1-phenylbut-2-en-1-one ( 4 ) (Scheme ), followed by azo coupling of compound 16 , or the reverse sequence of these reaction steps was answered by the finding that 3,4-dimethyl-2,2,6-triphenyl-1,3,2λ 4 -oxazaborine ( 16 ) does not react with diazonium salt.…”

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

“…Another possibility is the synthesis from b-enaminones and various derivatives of boron containing compounds (e.g. diphenylborinic acid or its ester, boron trifluoride or triphenylborane) [21].…”

The Problem Of Tautomerism

“…This is due to the fairly moderate propensity of silicon to pentacoordination and it, consequently, a result of the transition structure XXIV c. But in other organometallic derivatives of acetylacetone such as antimony [101,102], boron [103], lead and tin [104] derivatives as well as in transition metal-chelate acetylacetonates [105,106], where strong intramolecular coordination exists, the bonds are totally averaged, and symmetrical structures XXV and XXVI are stable. This is due to the fairly moderate propensity of silicon to pentacoordination and it, consequently, a result of the transition structure XXIV c. But in other organometallic derivatives of acetylacetone such as antimony [101,102], boron [103], lead and tin [104] derivatives as well as in transition metal-chelate acetylacetonates [105,106], where strong intramolecular coordination exists, the bonds are totally averaged, and symmetrical structures XXV and XXVI are stable.…”