Münchnone
{{Short description|Organic compound}}
{{Chembox
| Name =
| ImageFile = Munchnone_parent_compound.png
| ImageSize = 100px
| ImageCaption = Munchnone parent compound
| IUPACName = 1,3-oxazol-5-ol
| OtherNames =
| Section1 = {{Chembox Identifiers
| CASNo = 1044758-89-5
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID = 11455991
| DTXSID = DTXSID001018795
| PubChem = 12313816
| StdInChI=1S/C3H3NO2/c5-3-1-4-2-6-3/h1-2,5H
| StdInChIKey = IUNPZDITMZHUQF-UHFFFAOYSA-N
| SMILES = C1=C(OC=N1)O
}}
| Section2 = {{Chembox Properties
| C=3 | H=3 | N=1 | O=2
}}
}}
Münchnone (synonyms: 1,3-oxazolium-5-oxide; 1,3-oxazolium-5-olate; anhydro-5-hydroxy-1,3-oxazolium hydroxide; 5-hydroxy-1,3-oxazolium hydroxide, inner salt; oxido-oxazolium) is a mesoionic heterocyclic aromatic chemical compound, with the molecular formula C3H3NO2. The name refers to the city of Munich, Germany ({{Langx|de|München}}), where the compound and its derivatives were first discovered and studied.{{Cite journal |last1=Reissig |first1=Hans-Ulrich |last2=Zimmer |first2=Reinhold |date=2014-09-08 |title=Münchnones-New Facets after 50 Years |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.201405092 |journal=Angewandte Chemie International Edition |language=en |volume=53 |issue=37 |pages=9708–9710 |doi=10.1002/anie.201405092|pmid=25045012 |url-access=subscription }}
Synthesis and reactivity
The first preparation of a münchnone derivative was reported in 1959 by Lawson & Miles by cyclodehydration of 2-pyridone-N-acetic acid with acetic anhydride.{{cite journal |last1=Lawson |first1=Alexander |last2=Miles |first2=D. H. |title=574. Some new mesoionic compounds |journal=Journal of the Chemical Society (Resumed) |date=1 January 1959 |pages=2865–2871 |doi=10.1039/JR9590002865}} The azomethine ylide reactivity of münchnones, and their reaction with alkynes in the synthesis of pyrroles, was first published by Huisgen et al.{{Cite journal |last1=Huisgen |first1=R. |last2=Gotthardt |first2=H. |last3=Bayer |first3=H. O. |date=February 1964 |title=Azlactones as 1,3-Dipoles; A New Pyrrole Synthesis |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.196401353 |journal=Angewandte Chemie International Edition in English |language=en |volume=3 |issue=2 |pages=135–136 |doi=10.1002/anie.196401353 |issn=0570-0833|url-access=subscription }}{{Cite journal |last1=Huisgen |first1=R. |last2=Gotthardt |first2=H. |last3=Bayer |first3=H. O. |last4=Schaefer |first4=F. C. |date=February 1964 |title=A New Type of Mesoionic Aromatic Compound and Its 1,3-Dipolar Cycloaddition Reactions with Acetylene Derivatives |url=https://onlinelibrary.wiley.com/doi/10.1002/anie.196401361 |journal=Angewandte Chemie International Edition in English |language=en |volume=3 |issue=2 |pages=136–137 |doi=10.1002/anie.196401361 |issn=0570-0833|url-access=subscription }} The Huisgen group followed up with a thorough investigation of the chemical properties, reactivity, and utility of münchnones towards the synthesis of many other products.{{Cite book |last1=Gingrich |first1=Henry L. |url=https://onlinelibrary.wiley.com/doi/10.1002/9780470187289.ch4 |title=Mesoionic Oxazoles |last2=Baum |first2=Jonathan S. |date=January 1986 |publisher=Wiley |isbn=978-0-471-86958-0 |editor-last=Turchi |editor-first=I. J. |edition=1 |volume=45 |pages=731–961 |language=en |doi=10.1002/9780470187289.ch4}}{{Cite book |last=Gribble |first=Gordon W. |title=Oxazoles: Synthesis, Reactions, and Spectroscopy, Part A |chapter-url=https://onlinelibrary.wiley.com/doi/10.1002/0471428035.ch4 |chapter=Mesoionic Oxazoles |series=The Chemistry of Heterocyclic Compounds |date=2003-07-25 |publisher=John Wiley & Sons, Inc. |isbn=978-0-471-39494-5 |editor-last=Palmer |editor-first=David C. |volume=60 |location=Hoboken, NJ, USA |pages=473–576 |language=en |doi=10.1002/0471428035.ch4}} As such, they are typically credited for the discovery of the münchnone class of molecules. While certain substituted münchnones are stable and easily isolated under ambient conditions, the majority are unstable, including the parent münchnone itself. Münchnones are typically used as 1,3-dipolar cycloaddition substrates in the synthesis of pyrroles by their in situ generation in the presence of alkynes.
