Chemospezifität und Regioselektivität bei der Cycloaddition von Diazoalkanen an 1 H ‐1,2‐Diazepine

Abstract

1H-I ,ZDiazepine 1 reagieren mit Diazoalkanen chemospezifisch, jedoch nur regioselektiv, an der 4-Doppelbildung zu ,,direkten" und ,,inversen" Pyrazolinodiazepinen (3,4,6 -21). Dabei nimmt die Reaktivitat von Diazomethan (DAM) uber Diazoethan (DAE) zu Diazoisopropan (DAP) deutlich zu, was mit MNDO-Rechnungen in guter Ubereinstimmung steht. Nach den AO-KOeffizienten der Grenzorbitale sollten diese konzertierten Cycloadditionen keine RegiospezifitBt, sondern nur eine gewisse Regioselektivitat aufweisen, was wiederum durch das Experiment bewiesen wurde. Von allen Edukten reagieren die beiden 1-Benzoyldiazepine 1 e und f am besten, wobei die ,,inversen" Addukte fur l e uberhaupt nicht und fur If nur in geringem AusmaBe auftreten. Eine Methylgruppe in 3-Stellung der Diazepine 1 hat allgemein zur Folge, daJ3 die Wannenkonformation der entsprechenden Diazepine starker ausgepragt ist, wobei die Regioselektivitat noch abnimmt . Chemospecificity and Regioselectivity during Cycloaddition Reactions of Diazoalkanes with lH-1,2-Diazepines1H-I ,2-Diazepines 1 react in a chemospecific way, but only regioselectively, at the 4-double bond with diazoalkanes to form "direct" and "inverse" pyrazolinodiazepines (3,4,6 -21). A dramatic rate increase is observed when going from diazomethane to diazoethane and to diazoisopropane, a result which agrees quite well with MNDO calculations. Considering the A 0 coefficients of the frontier MO's which come into interaction during these concerted cycloadditions, the cyclcadditions are unlikely to occur in a regiospecific manner; only a slight regioselectivity is predicted and found in most of the cases. 1-Benzoyldiazepines l e and f proved to be the fastest reacting educts with no formation of the "inverse" adducts with l e and only in poor yield with If. Diazepines bearing a 3-methyl group have a more pronounced boat-shaped conformation than their non-alkylated homologues. As a consequence, the regioselectivity of the 1,3-dipolar cycloadditions is decreasing. 1H-1,ZDiazepine als Synthone zum Aufbau von neuartigen polyheterocyclischen MolekulenVor einigen Jahren haben wir zusammenfassend uber die Herstellung und das chemische und physikalische Verhalten von 1H-1 ,ZDiazepinen berichtet l). Letztere gehen

Efficient and Flexible Synthesis of Highly Functionalised 4‐Aminooxazoles by a Gold‐Catalysed Intermolecular Formal [3+2] Dipolar Cycloaddition

“…On evaluating a number of procedures, we found that adapting Streith46a,b and Kakehi’s36 protocols afforded a practically straightforward and expedient method. This could be generally applied for more elaborate substrates bearing different acyl functional groups from readily accessible electrophiles.…”

A little about Pyrazolo[3,4-d][1,2]diazepine: simple sustainable synthesis, NMR identification and prototropic equilibrium

“…Based on our previous experience, we selected a modification of pyrazolo [3,4-d] [1,2]diazepin-8-one. Of all the known publications [6][7][8][9][10][11][12][13] , the simplest and most convenient way to obtain it is the hydrazinolysis of 3,5-diphenylpyrano [3,4-c]pyrazole-8(1H)-one [11] . This approach is characterized by the simplicity of the reaction scheme, the use of inexpensive reagents, and allows a broad modification of the initial molecule.…”

Synthesis of Pyrido[1,2-b]indazoles via Aryne [3 + 2] Cycloaddition withN-Tosylpyridinium Imides

“…Compound 1b: yield 58%; slightly yellow solid; mp 207À208 °C (lit. 18 mp 206 °C); 1 H NMR (400 MHz, CDCl 3 ) δ 8.60 (dd, J = 6.4, 1.0 Hz, 1 H), 7.83 (td, J = 7.8, 1.4 Hz, 1 H), 7.56 (apparent d, J = 8.2 Hz, 2 H), 7.48 (dd, J = 8.1, 1.5 Hz, 1 H), 7.43 (td, J = 7.7, 1.8 Hz, 1 H), 7.19À7.12 (m, 2 H), 2.43 (s, 3 H), 2.36 (s, 3 H); 13 C NMR (75 MHz, CDCl 3 ) δ 156. 3, 146.5, 141.3, 140.7, 138.0, 129.3, 128.0, 126.4, 123.9, 21.3, 19.9; LRMS (ESI) 285 (M + Na), 263 (M + H).…”