Flash Vacuum Thermolysis of N‐(3‐ and 4‐Pyridylmethylidene)‐tert‐butylamines: Mechanisms of Formation of Pyrrolopyridines and Naphthyridines

Abstract

Pyrrolopyridines and naphthyridines are formed by flash vacuum thermolysis (FVT) of 3‐ and 4‐pyridylmethylidene‐tert‐butylimines 8 and 15. Elimination of a methyl radical generates resonance stablized 2‐azaallyl radicals a1 and b1. The formation of pyrrolopyridines 9, 16 and 17 is rationalized in terms of cyclization of 1‐aziridinyl radicals a2 and b2. Formation of naphthyridine 10 from imine 8, and of 11 and 18 from imine 15, are in accord with cyclization of 1‐azaallyl radicals a6 and b9. Formation of naphthyridine 11 from 8, and of 10 and 19 from 15, indicate the operation of the spiro‐cyclization pathways forming intermediates a9 and b14. Formation of the 1,8‐naphthyridine 20 (3 %) indicates a rearrangement through aziridine b22 and biradical b23. DFT calculations at the CAM‐B3LYP/6‐311G(d,p) level support the proposed reaction mechanisms.

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

“…As mentioned in section , a 2-azaallyl radical was suggested as a precursor to a critical 2-azaallyl cation toward the oxidative cyclization of o -aminobenzaldimines to the corresponding 2-aryl quinazolines S (section , Scheme ). 2-Azaallyl radicals were also proposed as initial intermediates in the flash vacuum thermolysis (FVT) of various tert -butyl imines . For example, FVT of imine 275 generated indole 275 , in addition to several other products, and the preliminary intermediate was suggested to be the 2-azaallyl radical formed by ejection of a methyl radical from the tert -butyl group (Scheme D).…”

Preise des Royal Australian Chemical Institute: A. O'Mullane, B. J. Smith, M. G. Banwell, R. J. Payne, D. M. D'Alessandro und C. Wentrup / Preise der Schweizerischen Chemischen Gesellschaft: G. Gasser und N. Banerji

“…experimentell und theoretisch mithilfe der Photochemie, der Blitzvakuumthermolyse und mikrowelleninduzierter chemischer Reaktionen. In Chemistry—A European Journal hat er neue Reaktionen von N ‐ tert ‐Butyliminen vorgestellt6a und im European Journal of Organic Chemistry die Bildung von Pyrrolopyridinen und Naphthyridinen mithilfe der Blitzvakuumthermolyse 6b. Wentrup war Gründungsmitglied im Editorial Board von Chemistry—A European Journal .…”

Royal Australian Chemical Institute Awards: A. O'Mullane, B. J. Smith, M. G. Banwell, R. J. Payne, D. M. D'Alessandro, and C. Wentrup / Swiss Chemical Society Awards: G. Gasser and N. Banerji

“…using photochemistry, flash vacuum thermolysis, and microwave‐induced chemical reactions. He has reported in Chemistry—A European Journal on new reactions of N ‐ tert ‐butylimines,6a and in the European Journal of Organic Chemistry on the formation of pyrrolopyridines and naphthyridines by flash vacuum thermolysis 6b. Wentrup was a founding member of the Editorial Board of Chemistry—A European Journal .…”