Imine, benzophenone, reaction with

Imines are particularly useful reagents when hindered electrophiles are considered. In this context, A-(oc-methylbenzylidene)benzylamines have been described as alternatives to acetophenones. " Similarly A-methylbenzophenonimine serves as an alternative to benzophenone ° itself in reactions with 2-phenyl-5(477)-oxazolone 146 to prepare 2-phenyl-4-(a-phenylethylidene)- and 4-(diphenylmethyl-ene)-2-phenyl-5(4//)-oxazolone, respectively. 

Reaction with ketone and imine functionalities was studied in detail for silylene 85. Reaction of this silylene with ketones such as benzophenone, 3,3-dimethylbutan-2-one, and 2-adamantan-2-one afforded the disilaoxetane compounds 139 in high yields (Scheme 15). The formation of these products most likely occurs via a [2+1] cycloaddition to form a short-lived oxasilacyclopropane intermediate 140, which further reacts with a second silylene to form the final product C19970M4861, 1997PS537>. 

Benzophenone imine is commercially available and serves as an ammonia surrogate that reacts with aryl halides in high yields under standard palladium-catalyzed conditions. Catalysts based on both DPPF- and BINAP-ligated palladium give essentially quantitative yields in reactions with aryl bromides (Eq. (23)). These reactions can be conducted with either CS2CO3 or NaOtBu as the base [179, 180]. The products are readily isolated by chromatographic techniques or by crystallization. Alternatively, they can be cleaved to the parent aniline by addition of hydroxylamine, acid, or Pd/C [180]. 

Cyclopropylideneacetic esters, reaction with benzophenone imine, 57, 24... 

Photoreduction of benzophenone by primary and secondary amines leads to the formation of benzpinacol and imines [145]. Quantum yields greater than unity for reduction of benzophenone indicated that the a-aminoalkyl radical could further reduce the ground state of benzophenone. Bhattacharyya and Das confirmed this in a laser-flash photolysis study of the benzophenone-triethylamine system, which showed that ketyl radical anion formation occurs by a fast and a slow process wherein the slow process corresponds to the reaction of a-aminoalkyl radical in the ground state of benzophenone [148]. Direct evidence for similar secondary reduction of benzil [149] and naphthalimides [150] by the a-aminoalkyl radical have also been reported. The secondary dark reaction of a-aminoalkyl radicals in photo-induced electron-transfer reactions with a variety of quinones, dyes, and metal complexes has been studied by Whitten and coworkers [151]. 

Primary amines. Copper(I)-catalyzed Grignard reaction with the reagent gives (V-substituted imines. Acid hydrolysis releases the primary amines and the bis(trifluoromethyl)benzophenone. 

A few years ago Cahard reported a series of studies on the use of immobilized cinchona alkaloid derivatives in asymmetric reactions with phase-transfer catalysts [17[. Two types of polymer-supported ammonium salts of cinchona alkaloids (types A and B in Scheme 8.4) were prepared from PS, and their activity was evaluated. The enantioselectivity was found to depend heavily on the alkaloid immobilized, with the type B catalysts usually giving better results than the type A catalysts. By performing the reaction in toluene at -50 °C in the presence of an excess of solid cesium hydroxide and 0.1 mol equiv of catalyst 10, benzylation of the tert-butyl glycinate-derived benzophenone imine afforded the expected (S)-product in 67% yield with 94% ee, a value very close to that observed with the nonsupported catalyst. (Scheme 8.4, Equation b) Unfortunately-and again, inexplicably-the pseudoenantiomer of 10 proved to be much less stereoselective, affording the R)-product in only 23% ee. No mention of catalyst recycling was reported [18]. 

The reactions of 1,1-dimethyl-2,2-bis(trimethylsilyl)silene (54) with carbonyl compounds such as acetone and ethyl acetate, and particularly with benzophenone imine, are very much faster than its ene reactions with hydrocarbons such as isobutene244,246,266, pointing to the involvement of the nucleophilic lone pairs in the former case. 

Beier and Pastyrikova (13M1411) reported that SFs-substituted benzi-soxazoles such as 78a (see Section 2.5) can be used as precursors for the synthesis of other SFs-substituted heterocycles, such as quinolines (see Section 2.7) as well as for a synthesis of quinazohnes. For example, reduction of ben-zisoxazole 78a using iron in aqueous AcOFl resulted in an excellent yield of ori/jo-aminobenzophenone 100. Reaction of benzophenone 100 with excess benzylamine provided the corresponding intermediate imine (not shown), which in the presence of i-BuOOH and catalytic iodine gave... 

Imines also undergo [2-I-2-I-2] cycloaddition reactions with isocyanates. Usually, one equivalent of the imine reacts with two equivalents of the isocyanate. For example, heating of an excess of azomethines or benzophenone anils with isocyanates affords six-membered ring [2+2- -2] cycloadducts (see Section 3.3.1.4). This reaction proceeds in a stepwise manner, as indicated by the formation of different cycloadducts when different isocyanates are used. Also, reaction of A-alkyl- and A-aryl formamidines with alkyl- or aryl isocyanates on heating or in the presence of zinc chloride as the catalyst gives 2 1 (iminedsocyanate) adducts. Some examples of these reactions are listed in Table 3.10. 

---