2-aryl-4-substituted-5 -oxazolones

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>. 

Alkyl(aryl)-2-(trifluoromethyl)-5(277)-oxazolones have been used as intermediates to prepare 2-(trifluoromethyl)pyrroles interesting compounds frequently used as insecticides and acaricides. The oxazolones react with electron-dehcient unsaturated compounds in the presence of a base. Reaction of 5(277)-oxazolones, usually with a substituted aryl ring at C-4, with a wide variety of alkynes and alkenes has given rise to numerous 2-(trifluoromethyl)pyrroles 56. For example,... 

Similarly, reaction of 4-aryl-2-(trihuoromethyl)-5(277)-oxazolones 52 with substituted azo compounds, for example, PhN=NC02Et affords (trihuoromethyl)dihy-drotri azoles." ... 

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). 

Ring opening of 2-aryl-5(477)-oxazolones 230, obtained from A-acylglycines, with A,A-dimethyl-2-aminoethanol provides choline esters of A-substituted amino... 

Synthesis oe Heterocyclic Compounds. In some cases, dehydroamino acids obtained from unsaturated 5(477)-oxazolones have been used as intermediates to prepare other heterocyclic compounds. For example, reaction of 2-benzoylamino-3-substituted-2-alkenoic acids 485 with alkyl or arylisothiocyanates affords 4-aryl-methylene-l,2-disubstituted-5-oxo-4,5-dihydroimidazoles 486 (Scheme 7.155). ... 

A -Acylamino aromatic ketones 790 can be prepared by arylation of saturated oxazolones in the presence of Lewis acids. Cyclodehydration of 790 leads to 2,5-diaryloxazoles 791. For example, saturated 5(4//)-oxazolones 789 from 7/-benzoyl-alanine or A-benzoylvaline undergo Friedel-Crafts arylation to afford substituted A-benzoylphenacylamines 790. In the presence of POCI3, 790 cyclizes to produce 5-aryl-2-phenyloxazoles 791 (Scheme 7.241). ... 

DC of imines and munchnones 145, in situ generated by treatment of 5(4//)-oxazolones with chlorotrimethylsilane, allowed a diastereoselective multicomponent synthesis of highly substituted imidazolines 146, containing a four-point diversity and two stereocenters. The process is applicable to aryl, alkyl, acyl, and heterocyclic substitutions and only the trans distereomers (with respect to and R ) of 146 were observed in almost all cases <03SI433>. 

Cycloadditions were found to be first-order reactions with respect to both 1,3-dipole and dipolarophile, in all cases so far investigated. There are some limits to kinetic studies of these reactions, as many 1,3-dipoles are very reactive substances. While aryl azides, diazoalkanes, some classes of azomethine imines (for instance sydnones), and some classes of azomethine oxides (nitrones) are stable and isolable, azomethine ylides are usually unstable, an exception being represented by a mesoionic oxazolone that has been used for kinetic investigations benzonitrile oxide has a very limited stability, although some substituted derivatives are stable for long periods nitrile imines are not commonly isolable because of their strong tendency to dimerise. 1,3-Dipoles of... 

To functionalize the C5 position, Williams and Fu developed a 2-phenylsulfonyl substituted oxazole. The C5 position of this oxazole can be cleanly deprotonated with LDA and trapped with either NIS or NBS to form the 5-iodo- or 5-bromo-2-phenylsulfonyloxazole in good yield. The same report details that the 2-phenylsulfonyl group can subsequently be displaced with alkyl, alkenyl, or aryl lithium reagents to form 2,5-disubstituted oxazoles efficiently. A triflate at the C5 position can be prepared from the corresponding oxazolone however, the oxazolone decomposes at room temperature, and Kelly reported that attempted Stille coupling with C5 triflates failed due to decomposition of the triflate. ... 

A series of imidazo[l,2-a]pyridines were prepared to study as anticonvulsants (Figure 1) (13CCL853).The most active imdiazo[l,2-cj]pyridines have a halo-substituted aryl ring at C-2 as well as a methyl group at C-8. Additional pharmacophores such as oxazolones, pyrazolones, imines, and... 

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