1,2,3‐Diazaborinine: A BN Analogue of Pyridine Obtained by Ring Expansion of a Borole with an Organic Azide

Abstract

A new pathway for the ring expansion reaction of antiaromatic boroles with organic azides is reported. While the reaction usually leads to 1,2‐azaborinines, it was diverted to the formation of a 1,2,3‐diazaborinine by changing the electronic characteristics of the reagents. The isolable azo‐azaborinine intermediate initially formed from the reaction of 1‐(2,3,4,5‐tetraphenylborolyl)ferrocene with 4‐azido‐N,N‐dimethylaniline gradually decomposed to a 1,2,3‐diazaborinine and benzonitrile. Both the spectroscopic properties and the reactivity of the heteroaromatic compound show analogies to pyridine, to which it is isoelectronic. Density functional theory (DFT) calculations provided insight into the mechanism of this unusual transformation.

Six-Membered Rings With Two or More Heteroatoms With at Least One Boron

“…10 Ring synthesis by transformation of another ring Among the ring syntheses by transformation of another ring, reactions of five-membered antiaromatic boroles appear most prominently in the literature. Braunschweig's group [150][151][152][153][154] and other workers 96,155,156 have exploited the reactivity of antiaromatic boroles, a class of π-conjugated five-membered boracycles, gaining access to 1,2-heteraborine derivatives. Examples are the preparation of highly substituted monocyclic 1,2-azaborines 125 (Scheme 56) 150 and 1,2-phosphaborines 126 (Scheme 57) 157 by ring expansion of boroles.…”

Diborane(4) Azides: Surprisingly Stable Sources of Transient Iminoboranes

“…Our group's experience with the surprising results of combining azides with reactive boron compounds prompted us to verify whether the stabilization provided by amine groups would allow us to isolate diboranes(4) bearing at least one azide group and whether this stabilization would prevent all further reactivity. Herein we report on the synthesis of several diazidodiboranes and their use as precursors to transient boryl‐iminoboranes, which yielded unprecedented dimers of NBNBN‐containing seven‐membered rings.…”

Diboran(4)azide als stabile Quelle für kurzlebige Iminoborane

“…So sind die Diborane(4) B 2 (NMe 2 ) 4 und B 2 (NMe 2 )X 2 deutlich stabiler als der Vorläufer B 2 X 4 (X=Halogen). Unsere überraschenden Ergebnisse bei der Kombination von Azidgruppen mit reaktiven Boreinheiten haben uns dazu veranlasst, zu untersuchen, ob der stabilisierende Effekt der Aminogruppe ausreichend groß für die Realisierung und Isolierung stabiler Diboran(4)azide ist. Hier berichten wir nun von der Synthese mehrerer Diboran(4)azide.…”