Rearrangements of 4-Quinolylcarbene, 3-Quinolylcarbene, and 2-Quinolylcarbene to 1-Naphthylnitrene and Cyanoindenes by Falling Solid Flash Vacuum Pyrolysis

Abstract

The relationship between 4-quinolylcarbene 17, 3-quinolylcarbene 21, 2-quinolylcarbene 25, and 1-naphthylnitrene 35 has been explored experimentally and computationally. The diazomethylquinolines generated from (5-tetrazolyl)quinolines or 1,2,3-triazolo[1,5-a]quinoline by conventional flash vacuum pyrolysis (FVP) were observed by IR spectroscopy. The carbenes were generated by falling solid flash vacuum pyrolysis (FS-FVP). 4-Quinolylcarbene 17 was found to rearrange to 3-quinolylcarbene 21 and then to 2-quinolylcarbene 25, and finally via 1-naphthylnitrene 35 to 1-cyanoindene 36, which then isomerizes to 3- and 2-cyanoindenes 12 and 13. The thermal rearrangement of 2-quinolylcarbene to 1-naphthylnitrene was verified by ESR spectroscopy. The reaction mechanism has been elucidated with the help of calculations of the structures and energies of the quinolylcarbenes and 1-naphthylnitrene and the intervening aza-benzobicyclo[4.1.0]heptatrienes, aza-benzocycloheptatetraenes, and aza-benzocycloheptatrienylidenes and the transition states connecting them at the B3LYP/6-31G* level. The nonobserved 1,2-hydrogen shifts in aza-benzocycloheptatetraenes/aza-benzocycloheptatrienylidenes are found to have very high activation barriers.

Isomer-Selective Threshold Photoelectron Spectra of Phenylnitrene and Its Thermal Rearrangement Products

“…Subsequent collisional stabilization and formation of the thermodynamically most stable isomer 8 does not occur due to low pressure in the high-vacuum chamber. The mixture is subsequently ionized and detected, which is in agreement with previous experiments using the same reactor. , It is worth noting that the equivalent naphthylnitrenes form a mixture of 2- and 3-cyanoindenes, with traces of 1-cyanoindene, while pyrolysis of 9-azidophenanthrene yields mostly 9-cyanofluorene, which further substantiates our findings. , …”

“…58,59 It is worth noting that the equivalent naphthylnitrenes form a mixture of 2-and 3-cyanoindenes, with traces of 1-cyanoindene, while pyrolysis of 9-azidophenanthrene yields mostly 9-cyanofluorene, which further substantiates our findings. 60,61 ■ CONCLUSION Obtaining reliable spectroscopic data on reactive intermediates is challenging due to the elusive nature of the intermediates, but these data are essential to understand these species. Phenylnitrene 1, a fundamental reactive intermediate in organic chemistry, was produced by FVP of azide 2 at 480 °C and characterized by mass-selected threshold photoelectron spectroscopy.…”

Ring Contraction in Arylcarbenes and Arylnitrenes; Rearrangements of 1- and 3-Isoquinolylcarbenes and 2-Naphthylnitrene to Cyanoindenes

“…The related FVP reactions of 1-naphthyl azide, 1,2,3-triazolo­[1,5- a ]­quinoline, and 2-(5-tetrazolyl)­quinoline are described elsewhere. , …”

Flash‐Vakuumpyrolyse – Techniken und Reaktionen

“…[229] Die Vorrichtung lässt sich kontinuierlich und automatisch betreiben, und innerhalb relativ kurzer Zeit kçnnen leicht Dutzende Gramm Feststoff umgesetzt werden. [230] FVP von Salzen war immer problematisch, und die FS-FVP-Methode hat sich als sehr nützlich erwiesen. [229] (Schema 15;s iehe auch Schema 1, bei dem flüchtige Isoxazolone einer Standard-FVP ausgesetzt sind), zur Generierung von Carbenen aus Te trazolen wie 119 und Tosylhydrazonsalzen wie 120 sowie zur Untersuchung der anschließenden Umlagerungen (Schema 16).…”

“…Um Va kuumschwankungen gering zu halten, ist es vorteilhaft, einen 8-L-Gasballast(oder grçßer) in die Leitung zur Hochvakuumpumpe einzubauen. Die Methode fand Verwendung fürdie Synthese von Acetylenen aus nichtflüchtigen Isoxazolonen 116-118[229] (Schema 15;s iehe auch Schema 1, bei dem flüchtige Isoxazolone einer Standard-FVP ausgesetzt sind), zur Generierung von Carbenen aus Te trazolen wie 119 und Tosylhydrazonsalzen wie 120 sowie zur Untersuchung der anschließenden Umlagerungen (Schema 16) [230]. FVP von Salzen war immer problematisch, und die FS-FVP-Methode hat sich als sehr nützlich erwiesen.…”