N-Methyl-C-phenylnitrone

N-methyl-C-phenylnitrone 213 nonlinear effect 260 normal electron-demand 215, 226, 302, 314... 

The salt 2 reacts with dimethyl acetylenedicarboxylate (DMAD) in the presence of CsF (or NaH) to form an isoxazolidine (4), which is formally derived from N-methyl-C-phenylnitrone. This reaction is believed to involve removal of the proton from the OH group of 2 to give b, which cycloadds with DMAD to provide c, the immediate precursor to 4. 

An outstanding comparison was made with the best known dipolarophi-le, dimethyl acetylenedicarboxylate (DMAD). The cycloaddition of N-methyl-C-phenylnitrone to adamantanethione is 1500 times faster than the addition to DMAD. As indicated in Scheme 74 the reaction is an equilibrium, leading to 56 44 ratio of product vs starting material. This equilibrium is shifted towards the left side for thiobenzophenones, as the cycloadduct formation breaks the conjugation, and thus these thiones do not appear to react with nitrones. Ab initio calculations were carried out to model the high reactivity of nitrones with thiocarbonyl compounds [257]. 

In the presence of potassium cyanide the N-methyl-C-phenylnitrone (112) takes part in yet a further cycloaddition reaction to give l-methyl-4,5-diphenylimidazole. With lithium metal the aldimine (113) forms a delocalized carbanion which will cyclize with aryl cyanides (Scheme 61) (80AHC(27)24l). See also Section 4.08.1.1.3. 

The [3+2] cycloaddition of nitrones to organonitriles bound to Pt(II), Pt(IV), or Pd(II), by use of a combination of the Lewis acidity of the transition metals and microwave irradiation, has been described in three independent reports. In the first example, Wagner et al. [95] reported that the [3+2] cydoaddition of N-methyl-C-phenylnitrone 130 to transition metal coordinated ( )-cirmamonitrile 129 occurred exclusively at the nitrile C=N bond, leading to bis-oxadiazoline complexes 132 in high yield (Scheme 11.33). In contrast, reaction of the nitrone 130... 

Figure 7.3 An example experimental electron density difference map for (Z)-N-methyl-C-phenylnitrone. The solid (dashed) contours are for an increased (decreased) electron density compared with a simple sum of noninteracting atomic densities. The inset in the top left shows a chemical structure of the same molecule in roughly the orientation in the contour plot, (Source Hibbs DE, Hanrahan JR, Hursthouse MB, Knight DW, Overgaard J, Turner P, Piltz RO, Waller MP (2003) Organic Blomolecular Chemistry 1 1034-1040.)...

Similarly small rate factors were obtained for 1,3-dipolar cycloadditions between diphenyl diazomethane and dimethyl fumarate [131], 2,4,6-trimethylbenzenecarbonitrile oxide and tetracyanoethene or acrylonitrile [811], phenyl azide and enamines [133], diazomethane and aromatic anils [134], azomethine imines and dimethyl acetylenedi-carboxylate [134a], diazo dimethyl malonate and diethylaminopropyne [544] or N-(l-cyclohexenyl)pyrrolidine [545], and A-methyl-C-phenylnitrone and thioketones [812]. Huisgen has written comprehensive reviews on solvent polarity and rates of 1,3-dipolar cycloaddition reactions [541, 542]. The observed small solvent effects can be easily explained by the fact that the concerted, but non-synchronous, bond formation in the activated complex may lead to the destruction or creation of partial charges, connected... 

The lone pair density observed in the (Z)-lV-methyl-C-phenylnitrone example discussed in Section 7.1.2 (Figure 7.3) shows a similar nonspherical distribution of charge around the O atom of the N—0 group. MO calculations on the nitrone would give nonbonding... 

The Reformatskii reaction of C-methyl-A -phenylnitrone, MeCH=N(Ph)—O", with ethyl bromoacetate furnishes the isoxazolidinone... 

X0-derivative (730) of this ring system is formed by Fischer indolization of the JV -methyl-iV -phenylhydrazone of the aldehyde 0CHCHMeCH2C02Et. 2-Methylfuran and C-benzoyl-iV-phenylnitrone, PhCOCH=N(Ph)—O, combine to form a mixture of the cyclo-adducts (731) and (732), together with the condensation product (733)." The iV-acyl-nitrone (734 Ad == 1-adamantyl), generated by oxidation of 7V-adamantane-l-carbonyl-A-methylhydroxylamine with silver sulphate, has been trapped as the 1,3-dipolar cyclo-adduct (735) with... 

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