Rearrangement nucleophilic addition followed

The reaction of amines with the 4-phenylazo derivative (228) results in their rearrangement into triazolines. Depending on the basicity of the amines and the size of the alkoxy group, three different triazolines (229. 230, and 231) are obtained (Scheme 117) (454. 459, 472). In all cases, the first step involves nucleophilic addition of the amine to the carbonyl group followed by ring opening and further ring closure. 

Nucleophilic addition to an acylsilane followed by a 1,2-Brook rearrangement and final trapping of the resulting carbanion in either an acylation or intramolecular... 

Nucleophilic addition of primary o.-R -allylamine to nitrone followed by a reverse Cope cyclization and Meisenheimer rearrangement gives the oxadiazi-nanes (426a-h) (Scheme 2.198). These reactions have found use for the preparation of oxadiazines, vicinal aminohydroxylamines, and diamines the latter are of particular interest as chiral ligands (683, 684). 

Fig. 6.25. Simplified mechanism of two degradation reactions between peptides and reducing sugars occurring in solids, a) Maillard reaction between a side-chain amino (or amido) group showing the formation of an imine (Reaction a), followed by tautomerization to an enol (Reaction b) and ultimately to a ketone (Reaction c). Reaction c is known as the Amadori rearrangement (modified from [8]). b) Postulated mechanism of the reaction between a reducing sugar and a C-terminal serine. The postulated nucleophilic addition yields an hemiacetal (Reaction a) and is followed by cyclization (intramolecular condensation Reaction b). Two subsequent hydrolytic steps (Reactions c and d) yield a serine-sugar conjugate and the des-Ser-peptide...

A plausible mechanism for the formation of 4 is rationalized on the basis that photolysis of 3 results in [2-1-2] cyclization to thietane 4 and is subsequently followed by rearrangement to thiolactone 5 (Scheme 6). Ring opening of the initially formed thietane 4 leads to a zwitterion, which is facilitated by lone pair electrons of nitrogen and oxygen atoms, and nucleophilic reaction of the thiolate anion to carbonyl carbon gives 5. For the tricyclic thietane 4a, nucleophilic addition of the thiolate anion is difficult, and results in the formation of stable thietane 4a. 

Saczewski and Debowski reported the l,4-diaza-3-oxa-Cope rearrangement of N-cyanate anilides (equation 52). Prototropic rearomatization of 176 and internal nucleophilic addition afford the corresponding benzimidazolinone 177, usually in moderate yields (32-78%). A concerted [3,3]-sigmatropic rearrangement is proposed based on the absence of para rearrangement product that usually results from homolysis or heterolysis of the N—O bond followed by recombination of the two radicals or ions. 

The 3 + 2-cycloaddition of commercially available Me3SiCHN2 with camphor sultam-derived dipolarophiles produces 3-trimethylsilyl-substitutcd-A1 -pyrazolincs which on acid treatment convert into optically active A2-pyrazolines.60 The nucleophilic addition of ethyl diazoacetate with /V-cthoxycarbonyl-/V-(2,2,2-trichlorocthylidcne)a-mine produces a new diazo intermediate (35), which by 1,3-dipolar cycloaddition followed by a sigmatropic rearrangement of the cycloadduct (36) furnishes a substituted pyrazole (37) (Scheme 13).61. 

Nucleophilic addition of anionic species to acylsilanes followed by the Brook rearrangement provides an efficient route to siloxy-substituted carbon nucleophiles valuable for further carbon-carbon bond formation. The reaction of... 

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