P-Methoxyacetophenone

Rearrangement across the double bond and possible anchimeric assistance involving carbon also has been investigated. Rappoport and Gal (134) have reported that the solvolysis of l-anisyl-2,2-diphenyl bromide, 224, in aqueous ethanol as well as in formic acid gave a,a-diphenyl-p-methoxyacetophenone, 225, as the only product i.e., no rearrangement product 226 was observed. 

Figure 3.9. Comparison of the experimental C=0 stretching Raman band obtained for p-methoxyacetophenone in cyclohexane (a), MeCN (b) and 50% H2O/50% MeCN (v v) (c) solvents with 532 nm excitation. (Reprinted with permission from reference [42]. Copyright (2005) American Chemical Society.)...

In a number of other cases it has been reported or implied that a single diastereomeric pinacol was formed, but the stereochemistry of the product was not determined these reports come from studies upon the electrochemical reduction of 3-acetylpyridine 87), p-acetamidobenzaldehyde 9I>, (3-di-methylaminopropiophenone 91 p-aminoacetophenone (which affords one pinacol in acid and the other in alkali)92), and the reduction of a mixture of p-dimethylaminoacetophenone and p-methoxyacetophenone to afford a mixed pinacol (87) 93>. 

Both materials were tested as catalysts in the anisole acylation (Scheme 1). The conventional Beta sample showed a slightly higher activity than the Beta (PHAPTMS). At 3 hours, the conversions were 26.8 and 22.8 % for the conventional and seed silanized catalysts, respectively. This behavior is explained as a consequence of the relatively small size of the anisole molecule, which allows this compound to diffuse without significant hindrances through the zeolitic micropores, and of the slightly weaker acidity of the Beta (PHAPTMS) sample. In both cases, p-methoxyacetophenone (p-MAP) was the main reaction product, being obtained with a high selectivity (> 97%). 

Treatment of 1 with p-methoxyacetophenone dimethyl acetal or a,/Fdimethoxystyrene, in the presence of pyridinium p-toluenesulfonate, gave the 2,3-acetal derivative. Although a new chiral center is generated in the product, a preference for a major isomer was observed (26). 

It is noteworthy that the absolute rate constants for the reaction of the benzophenone triplet with Et3SiH, n-C5HnSiH3, PhSiH3, and Cl3SiH have been measured by LFP,56 and comparison of the kinetic data with corresponding data for reactions of /-BuO radicals shows that these two transient species have a rather similar reactivity toward silanes. Furthermore, the xanthate and the p-methoxyacetophenone triplets were found to be more and less reactive, respectively, than the benzophenone triplet with Et3SiH.56 Similar behavior of excited states in reactions with tin hydrides is discussed in Section V. 

Mercury benzamide, 797 Mercury-sealed stirrers, 66-69, 220 Mesitaldehyde, 690, 701 Mesityl oxide, 353 Metaldehyde, 319 Metanilic acid, 586, 589 Methiodides, 660 Metho-p-toluenesulphonates, 660 p-Methoxyacetophenone, 733 p-Methoxybenzaldehyde, 690, 703 4-Methoxybenzoin, 708, 714 p-Methoxycinnamic acid, 719 p-Methoxyphenylacetic acid, 904, 905, 924, 925... 

Bredt s rule. In this way, 1-adamantyl p-methoxyacetophenone 86a was forced to yield only cyclobutanols 87a and 88a as photoproducts [281]. Whereas (benzene) solution phase irradiations of 86a yielded a 2.6 ratio of 87a/88a, the solid state photoproduct ratio, 0.5, favors the more sterically hindered cyclobutanol. X-Ray diffraction studies predict a chair-like y-hydrogen abstraction pathway for 86a (in contrast to the boat-like transition states of 82) in which the C=0-Ha distance is 2.67 A. Other abstractable hydrogens (Hb) are at least 0.3 A farther from the carbonyl oxygen (Scheme 44). If i-BR has a conformation which mimics that of the ketone, its least motion pathway favors formation of the more sterically hindered cyclobutanol 88a. 

The complexes ZnX [X = Q, Br or I L = [3,5-diphenyl-A4-(l,3,4-thiadiazoline)-2-ylidene]-p-methoxythioacetophenone or -p-methoxyacetophenone] have been isolated.856 On the basis of IR evidence the metal is believed to be trigonal bipyramidally coordinated with the ligand acting in a bidentate manner. The complexes are thus best formulated as [Znl XjX. 

Brunow and Sivonen (34) obtained similar results on a lignin model system, ethylguaiacylcarbinol. This compound did not undergo any oxidation when irradiated with near-uv light until p-methoxyacetophenone, a triplet sensitizer, was added to the solution. As the molar ratio of p-methoxyacetophenone to ethylguaiacylcarbinol was increased to 0.32 the rate of photooxidation of this benzyl alcohol increased. This result is consistent with the mechanism of light-induced yellowing shown in Scheme 3. 

For most carbonyl compounds, we expect to have two near-lying excited states in the triplet manifold, which are either n-n or tc-tc in character. The n-7T states frequently show radical-like behavior. Benzophenone is an example of such a molecule which has an n-7t triplet state in which we see occurrences of hydrogen abstraction and very efficient intersystem crossing. When the lowest state is the 71-71 state, largely centered on the aromatic part of the molecule, as in the case of p-methoxyacetophenone, the reactivity decreases significantly (8,9). With the nature of lignin and the nature of the model we have chosen, we are mostly interested in molecules which have this type of behavior. 

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