Ortho-substituted acetophenones

Table 7.1 and in general it can be stated that excellent isolated yields were obtained (>90%), using Xiao s method. Regarding the ortho substituted acetophenone examples (Table 7.1, last row),l acetylnaphthalene (not shown) was also an excellent substrate (90% yield, 87% ee). In addition to these successes with acetophenone derivatives, two aryl ethyl ketones were examined and provided similar high ee values. 

Placing two methyl groups ortho to the carbonyl of acetophenone should twist the phenyl out of the C=0 plane. The extent to which this affects gas- and solution-phase basicities of a series of /> /a-substituted acetophenones is reported.95... 

The copper-catalysed enantioselective 1,4-conjugate addition of Et2Zn to chalcones was investigated in the presence of a catalytic amount of Af,P-ferrocenyl ligand (179) with central and planar chirality under mild conditions (0 °C to room temper- ature). Chalcones with ortho-substituents (from ortho-substituted benzaldehydes and acetophenones) exhibited a dramatic improvement in the enantioselectivities (<92% ee).229... 

Pearson27 was to manipulate orientation in various ways to obtain any isomer desired. An example cited on 1, 32-33 is the meru-bromination of acetophenone, described by Pearson as a swamping catalyst effect. In the bromination of a phenol, para substitution ordinarily predominates over ortho substitution, but considerable increase in the proportion of ortho isomer can be achieved by operating at — 70° in the presence of a strongly basic aliphatic amine.28 The best procedure was to add bromine to a cold solution of f-butylamine in toluene, cool to about — 7(P, and add a phenol dropwise over a short period of time. By this procedure, phenol was converted by 1 equivalent of bromine into 2-bromophenol in 60% yield and by 2 equivalents of bromine into 2,6-dibromophenol in 87% yield. Tertiary amines such as DABCO and triethylamine serve also for enhanced o-bromination of phenols. Chlorination under the same conditions gave a mixture of o- and p-chlorophenols in the ratio 2 1. 

The intense absorption within the range 220-230 nm is due to the local excitation (L.E.) bonds of the benzenoid rings of the acetophenone chromophore. The absorption between 252-258 nm is caused by the electron transfer (E.T.) bond, which in case of the ortho- en meta substituted acetophenone chromophore is found between 240-270 nm. The benzenoid ring and one ketofunction are responsible for this E.T. bond. The absorptions between 265-280 nm and 285-290 nm are due to the E.T. bond of the benzoquinone chromophore. The absorption between 430-437... 

Murai et al. have reported that dihydridocarbonyl/> /5(tiiphenylphosphine)ruthenium (Ru) catalyzes the addition of the ortho C-H bonds of acetophenone across the C-C double bonds of olefins such as trimethylvinylsilane to yield ortho alkyl substituted acetophenones (7-3). We have shown that this reaction can be applied to achieve step-growth copolymerization (cooligomerization) of aromatic ketones and a,co-dienes. For example, reaction of divinyldimethylsilane and acetophenone catalyzed by Ru at 150°C yields copoly(3,3-dimethyl-3-sila-1,5-pentanylene/2-aceto-1,3-phenylene), =... 

The structure of the copolymers reported herein as determined by C, and Si NMR spectroscopy is consistent with predominant regioselective addition of the C-H bonds, which are ortho to the carbonyl group of the substituted acetophenones across the C-C double bonds of 1,3-divinyltetramethyldisiloxane or 3,3,6,6-tetramethyl-3,6-disila-l,7-octadiene such that the hydrogen becomes attached to the more substituted end of the double bond ( see experimental) as in Figure 1. 

In a time course study on the conversion of ( )-l-phenylethanol 13 (X=H), formation of acetophenone was observed to a maximum of around 20% during the conversion of (S)- to (R)- alcohol which occurred over 24 h to give (R)-13 in 96 % yield, 99% e.e. The effect of ring substitution on the efficiency of the dera-cemization was notable. While para substituents (Cl, OMe, Me) gave good results, ortho derivatives could not be deracemized and the biocatalyst showed little activity towards meta substituted compounds. On addition of allyl alcohol, improvements in e.e. were obtained, particularly for the conversion of l-(m-methylphenyl)ethanol (from 21 to 94% e.e.). However these improvements did appear to be at the expense of yield (89% diminished to 55%). The authors sug-... 

The carbonyl carbon in the acetophenone carries a partial positive charge because oxygen is more electronegative than carbon. This partial charge is illustrated in the first contributor to the intermediates for ortho or para substitution. Note that positive charges appear on adjacent atoms in these contributors - an unfavorable situation. No such contributor appears in the intermediate for meta substitution. Thus meta substitution predominates. 

From B. Pandey s research group comes a straightforward photochemical method for the synthesis of spirocyclic compounds. An intramolecular hydrogen abstraction by an excited enone group is followed by radical combination. It is remarkable that no product arising from photoenolization and subsequent cyclization was observed. This is usually observed in ortho-alkyl substituted benzophenone and acetophenone derivatives. 

Soon afterward, MacMillan s group properly explored this organocatalytic reductive amination, observing that the ortho-triphenylsilyl phosphoric acid 17n in the presence of 5-A MS facilitates the desired coupling of acetophenone and 4-OMe-aniline in high conversion and with excellent levels of enantiocontrol at 40 C (87% yield, 94% ee) [55]. Authors report also the reduction of the pyruvic acid-derived cyclic imino ester with excellent enantioselectivity. However, implementation of the corresponding ethyl-substituted imine resulted in a dramatic decrease in... 

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