Benzophenone, directed reaction

Benzophenone, directed reaction with acetaldehyde, 50, 68 1,4-Benzoquinone, 2,3-dichloro-5,6-dicyano-, (DDQ), aroma-tization with, 54, 14 Benzoylacetone, from acetophenone and acetic anhydride,... 

Benzophenone, directed reaction with acetaldehyde, 50,68 Benzoylacetone, from acetophenone and acetic anhydride, 51, 93... 

The tetrahydrofuran was dried by distilling from lithium aluminium hydride and then from sodium benzophenone ketyl (generated by adding small pieces of sodium metal and benzophenone) directly into the reaction flask. A blue-black color of the ketyl solution indicates dryness. The checkers purified tetrahydrofuran by distillation from sodium hydride dispersion under nitrogen, and used it immediately. 

With m-nitroanisole in liquid ammonia the benzophenone-sensitized reaction yields inter alia 2-methoxy-4-nitroaniline as a product and no m-nitroaniline, which is formed in very high yield upon direct irradiation in liquid ammonia as well as in NH3/CH3OH. In the latter instance l/4> varies linearly with 1/[NH3], suggesting that the reaction is either singlet or triplet but not of a mixed type. 

Diaryl ketimines, Ar1C=NH. The patent literature has described the preparation of (C6H5)2C=NH by direct reaction of benzophenone with ammonia, but this route has not been investigated further. Actually, a number of diaryl ketimines can be obtained in >95% yield by reaction of a diaryl ketone with liquid ammonia and a catalytic amount of ammonium chloride in THF in a sealed tube at 120° (60 bar). 

The photolysis of benzoyl azide can be sensitized efficiently by benzophenone" . Other conventional sensitizers such as naphthalene, triphenylene and anthraquinone have been reported to have only a small effect on the photoreaction, diazo-iso-butyronitrile and fluo-rene to have none. In the benzophenone-sensidzed reaction, where triplet nitrenes are formed directly, the only reaction product in alcohol soludon is benzamide, which is obtained in quandtadve yield. This demonstrates again the different chemistry of singlet and triplet nitrene routes in azide photolysis. 

Moreover, benzophenone photosensitization with the seven-membered, 2-phenyl material succeeded, but relatively inefficiently. These are obviously only qualitative results and must be verified by careful quantum yield determinations. Nonetheless, the apparent order of reactivity in both direct and benzophenone-sensitized reactions is acyclioseven ring>six ring>five ring. (M. Tabet, W. Baik, Y.W. Wu, unpublished results, this laboratory). 

The PFR of A-chloroacetylanthranylates afford benzophenones, whose direct reaction with ammonia gives 1,3-quinazolines. Alternatively, treatment with potassium iodide before addition of ammonia leads to l,3-dihydro-2ff-l,4-benzodiazepin-2-ones [178]. A related synthesis of benzodiazepines is based on an initial PFR of anilides derived from ALBoc-Ala-OH (Scheme 31.18) [179]. 

Figure Bl.16.2. X-band TREPR spectra obtained at 0.1 ps after 308 mn photolysis of a fliiorinated peroxide dimer in Freon 113 at room temperature. Part A is the A/E RPM spectrum obtained upon direct photolysis part B is the E/A RPM spectrum obtained upon triplet sensitization of this reaction using benzophenone.

In the ketone method, the central carbon atom is derived from phosgene (qv). A diarylketone is prepared from phosgene and a tertiary arylamine and then condenses with another mole of a tertiary arylamine (same or different) in the presence of phosphoms oxychloride or zinc chloride. The dye is produced directly without an oxidation step. Thus, ethyl violet [2390-59-2] Cl Basic Violet 4 (15), is prepared from 4,4 -bis(diethylamino)benzophenone with diethylaruline in the presence of phosphoms oxychloride. This reaction is very useful for the preparation of unsymmetrical dyes. Condensation of 4,4 -bis(dimethylamino)benzophenone [90-94-8] (Michler s ketone) with AJ-phenjl-l-naphthylamine gives the Victoria Blue B [2580-56-5] Cl Basic Blue 26, which is used for coloring paper and producing ballpoint pen pastes and inks. 

Intermolecular photocycloadditions of alkenes can be carried out by photosensitization with mercury or directly with short-wavelength light.179 Relatively little preparative use has been made of this reaction for simple alkenes. Dienes can be photosensitized using benzophenone, butane-2,3-dione, and acetophenone.180 The photodimerization of derivatives of cinnamic acid was among the earliest photochemical reactions to be studied.181 Good yields of dimers are obtained when irradiation is carried out in the crystalline state. In solution, cis-trans isomerization is the dominant reaction. 

As with 2-cyclopentenone, the ratio (70) (71) varies with the molar concentration of the enone, the head-to-head dimer (71) becoming increasingly important at higher concentrations/133 This reaction is efficiently sensitized by acetophenone, benzophenone, thioxanthone, and naphthalene. The same enone concentration effect was observed in the sensitized photo-dimerization as in the direct photolysis. Similarly, quenching of the dimerization by piperylene was not accompanied by a change in dimer ratio. Systematic... 

Dimers (73) and (74) were formed in approximately equal amounts in all cases, although, as in the cases of 2-cyclopentenone and 2-cyclohexenone, the relative amount of (72) (either cis-syn-cis or cis-anti-cis) was found to vary substantially with solvent polarity. As in 2-cyclopentenone, this increase in the rate of head-to-head dimerization was attributed to stabilization of the increase in dipole moment in going to the transition state leading to (72) in polar solvents. It is thought that the solvent effect in this case is not associated with the state of aggregation since a plot of Stem-Volmer plot and complete quenching with 0.2 M piperylene indicate that the reaction proceeds mainly from the triplet manifold. However, the rates of formation of head-to-head and head-to-tail dimers do not show the same relationship when sensitized by benzophenone as in the direct photolysis. This effect, when combined with different intercepts for head-to-head and head-to-tail dimerizations quenched by piperylene in the Stem-Volmer plot, indicates that two distinct excited triplet states are involved with differing efficiencies of population. The nature of these two triplets has not been disclosed. 

Comparison of these experimental results with the calculated charge densities (S0 and Si) at the 2 and 3 positions (Table 11.5) shows that this is the expected result. Except for those compounds discussed below, the failure to observe quenching with triplet quenchers and reaction in the presence of a photosensitizer indicated singlet reactions. Compound (89) was found to also undergo benzophenone-photosensitized substitution, indicating that the triplet state of this compound is also reactive. The reaction, however, was less clean than that observed in the direct photolysis. Similarly, 1,6-dinitro-naphthalene was found to undergo both direct and benzophenone-photosensitized substitution ... 

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