1,721,132 research outputs found
Norbornene Amino Acids : Versatile Synthons for the preparation of constrained amino acids
No full textα-Pyranones; I. Reaction of 4-ethoxy and 4-chloromethylene-2-phenyl-5(4H)-oxazolone with ethyl 3-oxo-4-(triphenylphosphoranylidene)butyrate: A new synthesis of 2H-pyran-2-one compounds
No full textThe reaction of 4-ethoxymethylene-5(4H)-oxazolone (2a) with ethyl 3-oxo-4-(triphenylphosphoranylidene)butyrate (1) affords ethyl 3-benzoylamino-2-oxo-6-triphenylphosphoranylidenemethyl-2H-pyran-5-cah boxylate (3). Starting from the corresponding 4-chloromethylene compound 2b and 1, besides 3, ethyl 3-benzoylamino-6-[2-(4,5-dihydro-5-oxo-2-phenyl-4-oxazolylidene)-1-(tr iphenylphosphoranylidene)ethyl]-2-oxo-2H-pyran-5-carboxylate (5) is formed. The phosphorane 3 is a reactive synthetic intermediate for the preparation of ethyl 6-(1-alkenyl)-3-benzoylamino-2-oxo-2H-pyran-5-carboxylates 7 through reaction with aldehydes
Oxazolones. Part VI. Reaction of 5(4H)-oxazolones with nitrile imines: Synthesis of 1H-1,2,4-triazoles through [3+2] cycloaddition
No full text5(4H)-Oxazolones (1) react as dipolarophiles in [3+2] cycloadditions with nitrile imines generated from tetrazoles (2) in refluxing anisole affording two 1H-1,2,4-triazole derivatives (3) and diarylethylenes (4). © 1992
1,3-Dipolar cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide to (phenylsulfonyl)allenes
No full textCycloaddition Reactions : key reactions to build constrained carbocyclic and heterocyclic amino acids
No full textA highly diastereoselective approach to conformationally constrained serine analogues: Synthesis of an α-amino-β-hydroxycyclohexenecarboxylic acid and derivatives
No full textA diastereospecific synthesis of α-amino-β- hydroxycyclohexenecarboxylic acid (7) was found starting from 4- chloromethylene-5(4H)-oxazolone (1) which reacted with 2,3-dimethylbutadiene in the presence of EtAlCl2. The Diels-Alder reaction gave two diastereoisomeric cycloadducts 2 and 3, depending on the configuration of the starting dienophile 1. Compounds 2a and 3 were transformed into the ester 4 and the oxazoline 6, respectively, by reaction with MeOH and p-TSA. The reaction of 2a and 3 with dimethylamine in ethanol solution gave the corresponding amides 8 and 9, respectively, which were transformed into the bicyclic oxazoline 10 on reaction with Na2CO3 in acetonitrile. On acidic hydrolysis both oxazolines 6 and 10 were transformed into α-amino-β- hydroxycyclohexenecarboxylic acid (7) that includes the serine skeleton
A new synthetic procedure to spiro[cyclohexane-1,3′-indoline]-2′,4-diones
No full textA new synthetic pathway to spiro[cyclohexane-1,3′-indoline]-2′,4-diones was found starting from 3-chloromethylene-2-indolones 1 and Danishefsky's diene 2. Their synthesis consists of several steps involving the formation of the cycloadducts, the 6-chloro-4-trimethylsilyloxy-2-methoxyspiro[cyclohex-3-en-1,3′- indolin]-2′-one derivatives, transformed into spiro[cyclohexa-2,5-dien-1,3′-indoline]-2′,4-diones via 6-chloro-spiro[cyclohex-2-en-1,3′-indoline]-2′,4-dione intermediates. The reduction of spiro[cyclohexa-2,5-dien-1,3′-indoline]-2′,4-diones gave spiro[cyclohexane-1,3′-indoline]-2′,4-diones 7. Using a 'one pot reaction', starting from 1 and 2, compounds 7 were obtained in satisfactory overall yield. © 2003 Elsevier Science Ltd. All rights reserved
5‐Oxazolones, IV. Reactions of 5(4H)‐oxazolones with triphenylphosphonium methylides
No full textThe Wittig reaction of ethyl (triphenylphosphoranylidene)acetate (2a) with the carbonyl group of trisubstituted 5(4H)-oxazolones 1a–c afforded ethyl 5(4H)-oxazolylideneacetates 3a–c and triphenylphosphane oxide. Starting from oxazolones 1d–i and ylide 2a, methyleneoxazoles 3d, e and ethyl 5-oxazoleacetates 4a–f were obtained besides ylides 5a–e deriving from the nucleophilic attack of the ylide at 1 and subsequent opening of the oxazole ring. Oxazolones 1a–c reacted also with triphenylphosphonium phenylmethylide (2b) to yield methyleneoxazoles 3f,g and ylides 5f–h. By treating triphenylphosphonium methylide (2c) and -methoxymethylide (2d) with 1a–c only open-chain compounds 5i–k and 5l–n, respectively, were obtained
A convenient procedure for the 4-alkylation of 2,4-diphenyl-2-oxazolin-5-one under phase transfer conditions
No full textAlpha-diazocarbonyl-piperidine derivatives : chemoselective rhodium catalysed transformation
No full textSeveral natural compounds or compounds of biological interest contain the piperidine nucleus that, in many cases, is inserted in complex structures or simply condensed with other rings.
Our interest is address to the preparation of different piperidine systems using a very interesting chemistry that combines the use of α-diazocarbonyl compounds and rhodium (II) dimer catalysts.
Our studies were focused on the synthesis of piperidine derivatives, or their benzocondensed analogues as well as of more complex structures such as hexahidrobenzophenanthidine alkaloids or crinine derivatives.
Several piperidine, all functionalized with diazo-keto function, characterized by a different substitution pattern and stereochemistry, were used as starting materials. These key intermediates when treated with a rhodium catalyst afford electrophilic carbenes that could give a chemoselective C-H or N-H insertion, or reactions with an aromatic ring depending on the nature of the catalyst.
Simple diazoketo-piperidine afforded CH insertion giving tropone derivatives. More complex compounds could be obtained from tetrahydroisoquinoline derivative
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