Imines benzophenone

Another ring closure, presumably initiated by attack on the heteroatom, is the formation of 1,1,3-triphenylisoindoline from diphenyldichloromethane and benzophenone imine (Scheme 60) the ability of this compound to undergo a thermal 1,5-phenyl shift, thereby forming 1,2,3-triphenylisoindole, makes this an attractive overall synthetic route (64LA(673)96). 

Although the Lewis basicity of the nitrogen atom of imines is weak, the bis-alkynyl complex Os(C2Ph)2(CO)(P Pr3)2 also coordinates benzophenone imine to give the six-coordinate bis-alkynyl complex Os(C2Ph)2(CO)(NH=CPh2)(PI Pr3)2,... 

Ma and co-workers extended use of chiral guanidine catalysts to the addition of glycine derivatives to acrylates [121], Addition products were achieved in high yield with modest enantioselectivity (Scheme 67). The ferf-butyl glycinate benzophenone imines generally provided better enantiomeric ratios than the ethyl glycinate benzophenone imines. Based on this observation, the authors hypothesized that an imine-catalyst complex determines the stereochemical outcome of the product. 

A Enantioselective Alkylation of Glycine Benzophenone Imine tert-Butyl... 

Unsubstituted 5-aminopyrimidine derivatives can also be prepared by the use of benzophenone imine 132 as the amine source, as demonstrated by the synthesis of 2- /7-butyl-5-pyrimidinamine 135 from the bromide 133 via the imine 134 <20060PD70>. 

N-Alkylnitrilium salts, prepared from benzonitriles and SbQs, acylate activated aromatic compounds under mild conditions. The resulting benzophenone imines can be cyclised and hydrolysed providing a good route to substituted xanthones (Scheme 34) <99 JOC4050>. 

Reductive coupling of benzalimines with a ytterbium metal occurs in a mixture of THF and HMPA at room temperature (Equation (66)). " The reaction proceeds via an azaytterbiacyclopropane complex. This kind of metallacycle is isolated in the case of a benzophenone-imine. 

Diazadienes have been shown by various groups to be suitable precursors of imidazoline derivatives by means of [4 + 1 ] cycloaddition reactions. In 1976 Matsuda and co-workers were able to cycloadd heterodienes 303, available from AMrimethylsilyl benzophenone imine and phenyl isocyanate, with cyclohexyl isocyanide to obtain 305 in 91% yield, after methanolysis of the initial adduct 304 [76JCS(P1)1523] (Scheme 67). 

Preparation of 0-Allyl-N-(9)-anthracenylmethylcinchonidinium Bromide as a Phase Transfer Catalyst for the Enantioselective Alkylation of Glycine Benzophenone Imine tert-Butyl Ester. 

Since the use of ammonia is not practical in transition metal catalyzed processes, the identification of its synthetic equivalents is of major importance. Benzophenone imine was found to couple with 3-bromopyridine readily under the above mentioned conditions (7.72.), The masking benzophenone was removed in transamination with hydroxylamine, which gave the desired 3-aminopyridine in 81% overall yield.92 Allylamine was also successfully employed as ammonia equivalent93... 

Several types of imine have been used as protective groups for amines in solution [230]. Most are stable towards bases, but can be hydrolyzed by acids. Benzophenone-derived imines can be prepared by treating support-bound aliphatic primary amines with benzophenone imine [148,260], but usually not by treatment with benzophenone. Polystyrene-bound benzophenone imines of glycine are sufficiently C,H-acidic to enable C-alkylation with alkyl halides [260,313] or Michael acceptors [314], and have mainly been used for this purpose (see Section 13.4.4). 

Allylic alkylations using a benzophenone imine of glycine methyl ester as a prochiral nucleophile and chiral phosphine ligands on palladium produced optical yields up to 57% (equation 354).436... 

Protected glycine derivatives have been used as the nucleophilic partner in enantioselective syntheses of amino acid derivatives by chiral PTC (Scheme 10.9). Loupy and co-workers have reported the addition of diethyl acetylaminomalonate to chalcone without solvent with enan-tioselectivity up to 82% ee [44]. The recent report from the Corey group, with catalyst 8a used in conjunction with the benzophenone imine of glycine t-butyl ester 35, discussed earlier, results in highly enantioselective reactions (91-99% ee) with various Michael acceptors (2-cyclo-hexenone, methyl acrylate, and ethyl vinyl ketone) to yield products 71-73 [21], Other Michael reactions resulting in amino acid products are noted [45]. 

Imine radical anions appear to be substantially more basic than their ketyl anion counterparts. In 1991, Zhan and Hawley reported that Ph2C=NH (generated via the electrochemical reduction of benzophenone imine) was a sufficiently strong base to depro-tonate weak carbon acids whose pK values were as high as 33185. 

Having optimized the catalytic enantioselective phase-transfer alkylation system, the group explored the scope and limitations. A variety of electrophiles were reacted with the benzophenone imine glycine tert-butyl ester 1 catalyzed by 5 mol% of the selected chiral dimeric PTCs, benzene-linked-l,3-dimeric PTC 37, 2 -F-benzene-linked-1,3-dimeric PTC 41, and naphthalene-linked-2,7-dimeric PTC 39, at reaction temperatures of 0°C or — 20 °C (Scheme 4.8). 

An important issue is the right choice of substrate 1 which functions as an anion precursor. Successful organocatalytic conversions have been reported with indanones and benzophenone imines of glycine derivatives. The latter compounds are, in particular, useful for the synthesis of optically active a-amino acids. Excellent enantioselectivity has been reported for these conversions. In the following text the main achievements in this field of asymmetric organocatalytic nucleophilic substitutions are summarized [1, 2], The related addition of the anions 2 to Michael-acceptors is covered by chapter 4. 

The use of benzophenone imines of glycine derivatives [19] as substrates in enantioselective organocatalytic alkylation has been developed toward an excellent method for preparation of a wide range of optically active a-amino acids with high enantioselectivity [1, 20],... 

The solid-phase synthesis of a-amino acids via alkaloid-catalyzed alkylation has been investigated by the O Donnell group [64, 65]. The solid-phase based synthetic approach is particularly useful for rapid preparation of a-amino acids for combinatorial application. The concept of this solid-phase synthetic approach, which comprises three key steps, is shown in Scheme 3.22 (for formation of (R) enantiomers). First, solid-phase bound glycine, 51, is converted into its benzophenone imine de-... 

The N-aryl imines 412 as protected anilines can be prepared by Pd-catalysed arylation of benzophenone imine with aryl halides using DPPF and BINAP as ligands, and aniline derivatives are obtained by deprotection [204a],... 

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