Amino acids aryl, preparation

Amino-4-aryl-5-acetic acid selenazoles were used by Knott (2l i as intermediates in the preparation of T.2, 4.6-naphthoselenazoles (21. 30, 31). 

Amino-4-aryl-selenazole-5-acetic acids were used by Knott for the preparation of naphtho-l, 2, 4,5-selenazoles. " ... 

Alkyl A-2-selenazolines, preparation. 259 Amidinium ion, ionic system of, 68 2-Amino-4-aryl-5-acetic acid selenazoles. 

In a separate study, Ohberg and Westman applied the same PS-DMAP in a one-pot microwave-induced base-catalyzed reaction of N-aryl and N-alkyl amino acids (or esters) and thioisocyanates for the library synthesis of thiohydantoins (Scheme 7.115) [136]. Thiohydantoins are of interest due to their ease of preparation and the range of biological properties associated with this heterocyclic ring system. The use of PS-DMAP as the base in this reaction gave slightly lower yields compared to when triethylamine (TEA) was used, but it resulted in a cleaner reaction mixture and an easier purification procedure. Cyclizations of a number of N-substituted... 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

Several reports have been made of a successful catalyzed addition/ substitution reaction resulting in direct attachment of phosphorus to aromatic rings. The preparation of mixed triarylphosphines has been accomplished by the reaction of tin- or silicon-substituted diphe-nylphosphines with aryl halides catalyzed by palladium reagents.74 A similar transformation has also been reported using nickel catalysis.75 The addition/substitution of diphenylphosphine to triflate functionalized phenolic linkages has been of use for the preparation of substances as analogues of tyrosine-related amino acid derivatives, accomplished with catalysis by palladium acetate (Equation 4.29).76... 

Recently, Borner and coworkers described an efficient Rh-deguphos catalyst for the reductive amination of a-keto acids with benzyl amine. E.e.-values up to 98% were obtained for the reaction of phenyl pyruvic acid and PhCH2COCOOH (entry 4.9), albeit with often incomplete conversion and low TOFs. Similar results were also obtained for several other a-keto acids, and also with ligands such as norphos and chiraphos. An interesting variant for the preparation of a-amino acid derivatives is the one-pot preparation of aromatic a-(N-cyclohexyla-mino) amides from the corresponding aryl iodide, cyclohexylamine under a H2/ CO atmosphere catalyzed by Pd-duphos or Pd-Trost ligands [50]. Yields and ee-values were in the order of 30-50% and 90 >99%, respectively, and a catalyst loading of around 4% was necessary. 

For the synthesis of perfectly dendronized sohd-phase polymers (Fig. 7.4) various dendritic structures were prepared based on amide connections [6]. For example, the naturally occurring amino acid lysine was used as a building block in creating a dendritic scaffold [33]. The synthesis of symmetrical tri-branching den-drimers on aminomethyl polystyrene macrobeads was also described in literature [34]. Recently, aryl ether dendrimers were prepared on hydroxymethyl polystyrene using a Mitsunobu reaction with 3,5-bis(acetoxymethyl)phenol [35]. 

Furthermore, Rueping and coworkers applied their reaction conditions to the cyanation of ketimines [54]. The use of A-benzylated imines derived from aryl-methyl ketones generally gave comparable yields, but lower enantioselectivities. However, this method furnished Strecker products bearing a quaternary stereogenic center, which are valuable intermediates for the preparation of optically active a,a-disubstituted a-amino acids. 

A number of substituted derivatives of 305 (cis, n = 1, 2 trans, n = 2), 306 cis or trans), 307, and 308 diendo and diexo) (R = Me, Et, Ph, substituted aryl) were prepared from the corresponding amino acids with isothiocyanate and acidic ring closure of the resulting thiocarbamide... 

Aryl ketones have also been reduced with triethylsilane and TiCl4. This method was used to prepare 7-aryl amino acids.121... 

Nitrones such as 102 gave 2-aryl-4-substituted-5(4//)-oxazolones 103 in the presence of acetic anhydride and triethylamine (Scheme 7.28). Selected examples of saturated-5(477)-oxazolones prepared via cyclization of amino acids are shown in Table 7.15 (Fig. 7.17). 

The logical consequence of using chiral acids as CDAs for amines, as outlined in Figure 6, is that (.R)- and (S)-l-(aryl)ethylamines (Table 1, entries 39 to 43) almost ideally fulfill the requirements of CDAs for separating chiral acids due to the difference in bulkiness of the substituents on the stereogenic centers. Amino acid derivatives such as L-leucinamide also serve well as CDAs. Both types have been highly appreciated as can be seen from the number of applications listed in Table 2. The condensation reactions between the chiral carboxylic acids and amines (CDAs) can be performed in several ways. However, the mildest but quantitative ones will be most appropriate in order to minimize the potential risks of racemization of any stereogenic center. Otherwise, erroneous analytical data or optically impure diaslereomers could be obtained in the course of the preparative separation. 

Chiral sulfinimines 236 are very useful intermediates for the preparation of enantiomer-ically pure primary amines 237 (equation 158) . This reaction has been applied to the synthesis of a-amino acids . For sulfinimines obtained from simple ketones, lithium reagents are preferable for the addition , while for cyclic ketones organomagnesium compounds gave the best results. Addition of alkyl and aryl Grignard compounds to sulfinimines, derived from 3- and 4-substituted cyclohexanones, proceeds with excellent diastereoselectivity, depending on the stereochemistry of the ring substituents rather than the sulfinyl group . 

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