Heterocyclen aus α‐nitroolefinen. XI . 1,2‐oxazine aus α‐nitroolefinen und β‐dicarbonylverbindungen

Abstract

Dihydro‐1,2‐oxazine 8 und 1,2‐Oxazine 12 werden aus Nitronsäuren der Addukte aus α‐Nitroolefinen und β‐Dicarbonylverbindungen (6) auf zwei Wegen hergestellt: A) Die Nitronsäuren 6 werden in einer siedenden Lösung von Harnstoff in Ethanol oder Methanol erhitzt. B) Die Nitronsäuren 6 werden mit einer wäßrigen Ammoniumchlorid/Natriumsulfid‐Lösung reduziert. 1H‐NMR‐ und 13C‐NMR‐Untersuchungen beweisen die Konstitutionen. Der Mechanismus wird diskutiert.

One-Pot Cyclizations of Dilithiated Oximes and Hydrazones with Epibromohydrin. Efficient Synthesis of 6-Hydroxymethyl-5,6-dihydro-4H-1,2-oxazines and Oxazolo[3,4-b]pyridazin-7-ones

“…They have been used, for instance, as intermediates during the synthesis of glycosidase inhibitor analogues , and of functionalized pyrroles . Although a number of synthetic approaches to 1,2-oxazines are known, − the development of alternative strategies is of considerable interest. Oxazolo[3,4- b ]pyridazin-7-ones have been previously prepared on the basis of cyclization reactions of 3-aminooxazolidin-2-ones …”

Product Class 14: Nitronic Acids and Their Derivatives

“…In the presence of catalytic amounts of potassium fluoride and tetrabutylammonium bromide, nitromethane and paraformaldehyde are transformed into 2-aci-nitropropane-1,3diol (14) in quantitative yield (Scheme 3). [16] Scheme 3 A Nitronic Acid from Nitromethane and Paraformaldehyde [16] N 14 HO O − + KF, TBAB, iPrOH, rt, 3 d 100% HO OH MeNO 2 + (CH 2 O) n 2-aci-Nitropropane-1,3-diol (14): [16] A mixture of paraformaldehyde (15.0 g, 500 mmol; based on formaldehyde equivalents), MeNO 2 (14.3 g, 234 mmol), KF (150 mg, 2.6 mmol), and TBAB (0.81 g, 2.5 mmol) in iPrOH (50 mL) under argon was stirred at rt for 3 d. The mixture was filtered through Celite and the solvent was removed to give a colorless solid; yield: 29.0 g (100%); mp 63.2 8C.…”

Update 1 of: Ionic Liquids in Heterocyclic Synthesis

“…479 Other syntheses rely on the Lewis acid catalyzed reaction of allenoximes, 480 the acid-catalyzed cyclization of cyclopropyloximes, 481 or the cyclization of γ-nitroketones. 482 Kitazume et al 483 introduced the use of ionic liquids in the synthesis of oxazines 168 from the reaction of benzaldehydes 8 with 2-aminobenzyl alcohols 167 as shown in Table 18. Ionic liquid was used in a molar ratio of 1:6 (reactant/ IL), and it was recovered and reused three times with no appreciable decrease in yield.…”

“…In addition, 1,2-oxazines have been prepared by base-mediated cyclization of γ-chloroximes and γ-sulfonyloximes . Other syntheses rely on the Lewis acid catalyzed reaction of allenoximes, the acid-catalyzed cyclization of cyclopropyloximes, or the cyclization of γ-nitroketones . Kitazume et al .…”