Rearrangement nitrogen-nucleophiles

The Lewis acid trimethylsilyl triflate brings about the rearrangement of 2,3-epoxyamines to the corresponding 2-trimethylsilyloxymethylaziridinium ions.38 Such intermediates react regiospecifically with nitrogen nucleophiles to form 1-substituted 2,3-amino alcohols with full stereochemical control. 

The conversion of an amide in this way is termed the Hofmann reaction or the Hofmann rearrangement. The mechanism of the reaction involves an intramolecular 1,2-carbon-to-nitrogen nucleophilic shift of the alkyl (or aryl) group... 

A series of 3-amino (or 3-N-substituted amino)-l,2,4-oxadiazoles 108 can be obtained in moderate to high yields by the photoinduced rearrangement of 3-acylamino-l,2,5-oxadiazoles (furazans) 106 irradiated in the presence of an excess of ammonia or aliphatic amines [64—66]. The reaction follows a fragmentation-cycloaddition route, with the initial formation of a nitrile and a nitrile-oxide the latter is attacked by a nitrogen nucleophilic reagent (ZH in Scheme 12.29), and the open-chain interme-... 

Buscemi, S., Vivona, N. and Caronna, T. (1996) Photoinduced molecular rearrangements. The photochemistry of some 1,2,4-oxadiazoles in the presence of nitrogen nucleophiles. Formation of 1,2,4-triazoles, indazoles, and benzimidazoles. Journal of Organic Chemistry, 61 (24), 8397-8401. 

Nucleophilic displacement of the chlorine atom of 3-chloro-1,2-benzisothiazole has proved to be a popular procedure. Boeshagen and Geiger34 have continued their earlier work on nitrogen nucleophiles, and now include carbon, oxygen, and sulfur nucleophiles.35 In some cases, rearrangements occur, as in the formation of 3-amino-2-acylbenzo[6]thiophenes (20) from reaction of 21 with methyl ketones. Similar results are obtained from the reaction of other carbon nucleophiles, and it has been suggested that attack may be either at the 3-carbon or the sulfur atom.36 The reaction of 3-chloro-1,2-benzisothiazole (8) with the anion of ethyl cyanoacetate, for example,... 

Phosgene reacts with oximes to form 0-(ch oroformyl) oximes 124, which, on addition of antimony pentachloride, undergo smooth Beckmann rearrangement with loss of carbon dioxide to give the nitrilium salts 125 almost quantitatively [66]. With oxygen or nitrogen nucleophiles, O-(chloroformyl) oximes 124 form symmetrical and unsymmetrical oxalyl derivatives. 

The reactions between enantiopure cyclohexene oxides and Irani-1,2-bromoacetates with nitrogen nucleophiles have been investigated using NMR spectroscopy and X-ray crystallography." The reactions are complex and appear to occur by a combination of 5 2, Sj 2, and [3.3]-sigmatropic rearrangements. 

A nitrogen nucleophile (98) reacts with ethynyl(phenyl)iodonium salt to give an ylide (99), which loses iodobenzene to give vinylidine (100). The vinylidine rearranges by 1,2-hydrogen shift to the corresponding alkyne in the usual way. ... 

Additionally, Schaumann demonstrated that this approach can be used in the S3Uithesis of pyrrolidine- and piperidine-2,3-diones. Treatment of bromoalkyl isocyanates with 2-lithio-2-TMS-l,3-dithiane provides, after Brook rearrangement and nucleophilic displacement of bromide, the corresponding lactams with moderate to good yields. Protection of the nitrogen followed by a two-step dithiane hydrolysis affords pyrrolidine- and piperidine-2,3-diones (eq 25) ... 

Nazarov-type Reactions. It has been shown that the highly Lewis acidic Sc(OTf)3 and Yb(OTf)3 can catalyze the Nazarov cyclization. Recently, Dy(OTf)3 has been err5>loyed to catalyze the rearrangement of furfural and furylcarbinol reagents. These rearrangements are proposed to terminate in Nazarov-type 47T electrocyclizations. A Dy(OTf)3-catalyzed formation of trans-4,5-diamino-2-cyclopenten- 1-ones fromfurfural and nitrogen nucleophiles has been disclosed (eq 5). ... 

Azide salts are a class of versatile nitrogen nucleophiles that can be readily employed as reaction partners in palladium-catalyzed allylic displacement reactions. A telling example was documented by Trost in the desymmetrization of bis-carbonate 51 to give azide 52 in an excellent 95% ee (Scheme 14.10) [66]. The fact that the reaction proceeds under mild conditions ensures that any undesired rearrangement of the allylic azide 52 is suppressed. 

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