Rearrangement amine oxides

Coumarins are known to have pronounced bioactivity. A rather new procedure for the synthesis of pyrrolo[3,2-c]coumarins uses a domino process in which an amine oxide rearrangement [61] is involved (Scheme 7.37) [62]. Reaction of the cou-... 

A tandem aza-Wittig/heterocumulene-mediated annulation route was developed for the efficient production of 6,7,8,9-tetrahydro-benzothieno[2,3-r/]-l,2,4-triazolo[l,5-a]pyrimidin-10(3F/)-ones <05S1601>, and an amine oxide rearrangement was key to the regioselective preparation of pyrrolo[2,3-J]pyrimidines <0581164>. Hexahydro-2-phenacylidene-pyrimidines gave -lactam fused 8-aroyl-2,3,4,5-tetrahydro-7-hydroxy-6//-pyrrolo[l,2-a]py-rimidine-6-ones when treated with (COCl), in the presence of NaH <05IJH87>, and methyl... 

Without the presence of the electron-releasing hydroxyl or dimethylamino group, the primary products of oxidation, amine oxides, rearrange... 

C. Rearrangements of /-Amine Oxides Rearrangements with Migration to an DEFICIENT Nitrogen A. Beckmann Rearrangement... 

Rearrangement, Aliphatic amine oxides without an ahphatic hydrogen atom P to the nitrogen undergo Meisenheimer s rearrangement when heated to give trisubstituted hydroxylamines. 

The N-oxide function has proved useful for the activation of the pyridine ring, directed toward both nucleophilic and electrophilic attack (see Amine oxides). However, pyridine N-oxides have not been used widely ia iadustrial practice, because reactions involving them almost iavariably produce at least some isomeric by-products, a dding to the cost of purification of the desired isomer. Frequently, attack takes place first at the O-substituent, with subsequent rearrangement iato the ring. For example, 3-picoline N-oxide [1003-73-2] (40) reacts with acetic anhydride to give a mixture of pyridone products ia equal amounts, 5-methyl-2-pyridone [1003-68-5] and 3-methyl-2-pyridone [1003-56-1] (11). 

Isoprene (2-methyl-1,3-butadiene) can be telomerized in diethylamine with / -butyUithium as the catalyst to a mixture of A/,N-diethylneryl- and geranylamines. Oxidation of the amines with hydrogen peroxide gives the amine oxides, which, by the Meisenheimer rearrangement and subsequent pyrolysis, produce linalool in an overall yield of about 70% (127—129). 

Other examples of [2,3] sigmatropic rearrangements involve amine oxides and diazenes ... 

This substance under the action of alkali passed into anhydrodihydro-protopine A, C20H19O4N, m.p. 120° (V), the amine oxide (VI) of which rearranges into protopine by the action of acids. 

The thermal rearrangement of 1,5-dienes 1 to yield the isomeric 1,5-dienes 2, is called the Cope rearrangemenC —not to be confused with the thermolysis of amine oxides, which is also named after Arthur C. Cope. 

The rearrangements of allylic sulfoxides, selenoxides, and amine oxides are an example of the first type. Allylic sulfonium ylides and ammonium ylides also undergo [2,3]-sigmatropic rearrangements. Rearrangements of carbanions of allylic ethers are the major example of the anionic type. These reactions are considered in the following sections. 

Rearrangement of Allylic Sulfoxides, Selenoxides, and Amine Oxides... 

A7-Ally] amine oxides represent the general pattern for [2,3]-sigmatropic rearrangement where X = N and Y = O The rearrangement provides O-allyl hydrox-ylamine derivatives. 

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