Oxadiazolines rearrangement

Ring enlargement of A-acyl compounds, generally observed with oxaziridines, is observed only occasionally with diaziridines. Under more forced conditions of acylation with acetic anhydride, oxadiazolines like (139) were obtained (76MIP50800). A 4-nitrobenzoyl derivative rearranged at room temperature (76JOC3229). 

A -1,3,4-Oxadiazoline, fluoromethyl-rearrangement, 6, 437 Oxadiazolines alkylation, 6, 431 irradiation, 6, 437 mass spectra, 6, 380 oxirane synthesis from, 7, 117-118 ring cleavage... 

In another example using the isomeric amidoxime substrate 61, the formation of the expected [3,3]-rearrangement product 63 was not observed (Scheme 6.22). Instead the Z-adduct 62Z cyclized to oxadiazoline 64. Interestingly, the E-adduct 62E rearranged to hydroxypyrimidinone 60 and imidazole 66 instead of 63. The rearrangement of the substrate 62E was proposed to occur via intermediate 65 via a [l,3]-sigmatropic rearrangement which, after cyclization, led to the observed products 60 and 66. 

There is no published example of a cyclopropanation of the double bond in chlorocyclopropylideneacetate 1-Me with retention of the chlorine atom. Thus, attempted cyclopropanations under Simmons-Smith [37] or Corey [38] conditions failed [25]. The treatment of the highly reactive methylenecyclopropane derivative 1-Me with dimethoxycarbene generated by thermal decomposition of 2,2-dimethoxy-A -l,3,4-oxadiazoline 26 (1.5 equiv. of 26,PhH, 100 °C,24 h),gave a complex mixture of products (Scheme 7) [39], yet the normal cycloadduct 28 was not detected. The formation of compounds 29 - 33 was rationalized via the initially formed zwitterion 27, resulting from the Michael addition of the highly nucleophilic dimethoxycarbene to the C,C-double bond of 1-Me. The ring closure of 27 to the normal product 28 is probably reversible, and 27 can rearrange or add a second dimethoxycarbene moiety and a molecule of acetone to form 33. 

Methoxy[(trimethylsilyl)ethoxy]carbene - obtained by thermolysis of the corresponding oxadiazoline 337 - reacts with Cgo in an unprecedented reaction pathway [383,384]. The expected methanofullerene-[2-i-l]-cycloadduct could not be observed. Instead the two dihydrofullerene adducts 338 and 339 were isolated (Scheme 4.69). They are formed by an unusual addition-rearrangement mechanism that includes the migration of the trimethylsilyl group. 

The nitrone (177) rearranges under the influence of heat to the oxadiazoline (178) (Scheme 77)... 

Ring opening by photolysis also occurs in the oxadiazoline ring. Srivastava and Clapp109 noted that a simple rearrangement [Eq. (44)] of 4-/3-ethoxyethyl-3-methyl-5-p-nitrophenyl-l,2,4-oxadiazoline to a substituted amidine (50) took place on a bench top in ordinary daylight or... 

Addition of dimethoxycarbene (generated by thermolysis of the corresponding oxadiazoline) to 9-fluorenone gave rise to the unstable oxirane (observed by H NMR).55 This species was shown to rearrange to the ester (41) by an intramolecular methoxy transfer from (42) [and not by a 5-endo-tet methyl transfer from (43)]. 

Thermolysis of 2-acetoxy-2-methoxy-5,5-dimethyl-A3-l,3,4-oxadiazoline affords acetoxy(methoxy) carbene.60 The thermal rearrangement of acetoxy(methoxy) car-bene to methyl pyruvate was studied by DFT at the B3PW91/6-31G(d,p) level. The conformation of the carbene was considered, as were competing fragmentations to radical pairs. The authors concluded that the reaction is a concerted 1,2-migration rather than a fragmentation-recombination process. 

Boyer, J.H. and Ellis, P.S. (1979) Fragmentation-rearrangement of A3-oxadiazolin-5- and 3-ones. Journal of the Chemical Society, Perkin Transactions , (2), 483-487. 

Sumengen, D. and Pelter, A. (1983) The preparation and rearrangements of 3,4-disubstituted l,2,4-oxadiazoline-5-thiones. Journal of the Chemical Society, Perkin Transactions 1, (4), 687-691. 

Rearrangement of Pyrazoles and Hydantoins to 1,3,4-Oxadiazoks 2-Methyl-4-aryl-l,3,4-oxadiazolin-5-one (30) is obtained by the... 

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