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From isothiazoles to new or known heterocycles via cycloaddition reactions
No full textFrom isothiazoles to new or known heterocycles via cycloaddition reactionsThe synthesis and chemical reactivity of 3-amino-isothiazole S-oxides have been studied by us for many years and important transformations and uses of these compounds have been found as precursors both of N- and/or S- containing heterocycles and of open chain compounds through ring opening reactions. In particular, 3-amino-isothiazole S-oxides have been demonstrated to be a versatile system and an effective reaction partners in cycloaddition reactions all of which occurred with high regioselectivity at the C-4-C-5 double bond.1 The resulting cycloadducts are susceptible to transformation in new or known heterocycles through the cleavage of one of the rings present in the primary cycloadduct. Their cleavage depends on several factors such as the reaction conditions and the substitution pattern. The combination of the cycloaddition reactions and ring transformation represents a good strategy affording mono or bicyclic compounds of both chemical and pharmacological interest. A survey of the synthetic possibility of this combination of reactions will be shown
α-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
Cycloaddition Reactions : key reactions to build constrained carbocyclic and heterocyclic amino acids
No full text2-amidinylindole-3-carbaldehydes: Synthesis of new tetracyclic compounds containing the pyrrolo[1,2-c]1,4-diazepine ring
No full text2-Amidinylindol-3-carbaldehydes bearing an alpha-alkoxycarbonyl substituent on the cyclic-tertiary amine moiety were prepared. Pyrolysis of these amidines in diethylenglycol-monoethyl ether produced mainly a pyrrolo[ 1',2'-1,2]-1,4-diazepino[5,6-b]indol-7,11-dione. A similar result was obtained starting from 2-amidinylbenzofuran-3-carbaldehyde
α-Pyrones. Part 4. synthesis of 3-benzoylamino-6-(indol- 2-yl)pyran-2-ones and their rearrangement to substituted azepino[1,2-a]indole-6- ones: Unusual neighbouring group participation
No full text6-(2-Nitrostyryl)pyran-2-ones 3 are converted into 6-(indol-2-yl)pyran-2-ones 4 by reduction of the nitro group with triethyl phosphite and consequent addition of the nitrene intermediate to the styryl double bond. Compounds 4 undergo a rather unusual, base-catalysed, rearrangement leading to azepino[1,2-a] indol-6-ones 5
Single step synthesis of 2,3-dialkyl-6-nitro-quinazolin-4(3H)-imines and 3,5-dialkyl-9-nitro-imidazo[1,2-c]quinazolin-2(3H)-ones
No full textAbstract—A single step synthesis of 2,3-dialkyl-6-nitro-quinazolin-4(3H)-imines and 3,5-dialkyl-9-nitro-imidazo-[1,2-c]-quinazolin- 2(3H)-ones from simple carbonyl compounds, primary amines or amino acid methyl esters and 2-azido-5-nitro-benzonitrile was developed. Key intermediates were N,N0-disubstituted amidines obtained by rearrangement of 4,5-dihydrotriazoles; the new heterocyclic rings were formed by spontaneous intramolecular reaction of the amino and cyano groups which are present in the intermediates
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
Chemoselective and enantioselective synthesis of 3-aminoisothiazolo S-oxides
No full textChemoselective and enantioselective synthesis of 3-aminoisothiazolo S-oxidesThe main scope of our project is the chemoselective oxidation of 3-amino-isothiazoles 1 affording the new 3-amino-isothiazole S-oxides 3. The number of oxidizing reagent used for the oxidation of sulfides to sulfoxides are many and varied but few have general or broad application. Many oxidizing reagents are too reactive over-oxidizing sulfoxides to sulfones, with other the chemoselectivity is poor or they give undesiderable side reactions. Additional limitations include slow reaction rates, the necessity for careful control of the reaction parameters, instability and expense. Among the oxidizing reagents available we found N-sulfonyloxaziridines 2 as the more effective and selective reagents affording 3 in satisfactory yield (61-64%) together with minor amount of the corresponding sulfones 4 (10-15%)
Much efforts has also been devoted to the development of methodology for the preparation of optically active sulfoxides. Several kind of chiral sulfonyloxazirides have been tested affording optically active sulfoxides with satisfactory yield and ee% depending on the hindrance of oxaziridines. As an example the reaction between 1 and 4a or 4b is reported
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