Azobrücken aus Azinen, I. Isopyrazole als elektronenarme Diene zur Synthese von 2,3‐Diazabicyclo[2.2.1]heptenen

Abstract

Es wird ein allgemeines Prinzip zur [4@ + 21-Cycloaddition beschrieben, bei dem protonierte cyclische Azine als elektronenarme Diene in einer Diels-Alder-Reaktion mit inversem Elektronenbedarf mit elektronenreichen Olefinen reagieren. Als Beispiele dienen die Derivate 2 s und 2b des Isopyrazols. Die katalytische Aktivitat verschiedener Sauren wird studiert und die Reversibilitat der Cycloaddition nachgewiesen. Es sind auch Cycloaddukte (endo-14a und endo-14b) mit parallelen C = C/N = N-Bindungen zuganglich, die charakteristische UV-und NMR-Spektren zeigen. Azo Bridges from Azines, I Isopyrazoles as Electron Deficient Dienes for the Synthesis of 2,3-Diazabicyclo[2.2. llheptenesA general principle for [4@ + 21 cycloaddition in Diels-Alder reactions with inverse electron demand is described, where protonated azines serve as electron deficient dienes and electron rich olefins as dienophiles. This reactivity pattern is illustrated by isopyrazoles 2a and 2b. The catalytic activity of some acids is studied and the reversibility of the cycloaddition is proved. Inter alia cycloadducts (endo-14a and endo-14b) are obtained with parallel C = C / N = N bonds, which show characteristic features in their UV and NMR spectra. Diazetidinderivat erlaubten'). Nach Aufklarung des komplexen Reaktionsverlaufs lieR sich inzwischen ein breit anwendbares Syntheseprinzip entwickeln)), nach dem zahlreiche Vertreter der Einfuhrung und Zielsetzung der Serie

1H, 13C and 15N NMR investigation of a new, condensed hexahydro‐1,3,5‐triazine

“…The long-range 1 H, 13 C-and 1 H, 15 N-HMBC connectivities of methyl protons provided NMR of a condensed hexahydro-1,3,5-triazine the main fragments of the skeleton. Considering the connectivities of nuclei obtained from COSY, TOCSY and HMQC-TOCSY measurements, we managed to identify two different building blocks, corresponding to three condensed cyclopenta [4,5]pyrazoline moieties, that form a central hexahydro-1,3,5-triazine ring. A priori there are two isomeric structures to be considered, namely the symmetrical all-cis and the trans-cis-cis isomer.…”

“…5 For both, only the diastereomer with one trans bridgehead hydrogen atom was reported. 4,5 Analogously, the 1,3,5-triazine 9 results from the parent 1,2-diazacycloheptatriene by trimerization of its cyclic diazanorcadiene valence isomer; again the diastereomer with one trans bridgehead hydrogen atom is favored. 5 Presumably, steric effects in the trimerization of the aldimine-type precursor disfavour the all-cis structure at the ring junctions.…”

“…Also in the attempted preparation of aldimine-type isopyrazoles, trimerization to the more complex 1,3,5-triazine occurred, which led to 7b from 4,4-dimethyl-4H-pyrazole 4 and 8b from 3,4,4-trimethyl-4H-pyrazole. 5 For both, only the diastereomer with one trans bridgehead hydrogen atom was reported.…”

Preferred Formation of anti‐Housane (Retention) in the Sensitized Photodenitrogenation of Cyclopentane‐Annellated DBH‐Type Azoalkanes through Long‐Range Steric Effects in the Cyclization of the Triplet Cyclopentane‐1,3‐diyl Diradicals

“…The known azoalkanes 1a , b were prepared according to the Hünig route 9. Upon irradiation with the 351‐nm line of an argon‐ion laser, their denitrogenation led exclusively to the syn and anti diastereomers of the housanes 2a , b .…”

Azo‐Borane – eine neue Verbindungsklasse

“…C 70.67 H 10.28 N 13.73 Gef. C 70.35 H 10.30 N 13.30 (4ac,8ac) ,8ac) -1,4,4a,5,6,7,8,8a-Octahydro-l,4,iO,iO-tetramethyllr, 4~;5t,8t-dimethanophthalazin-6t-ol (9) und 8: Zu 3.00 g (13.9 mmol) 791 in 25 ml trockenem Tetrahydrofuran werden langsam…”