1,721,009 research outputs found
Stereoselective synthesis of highly functionalised tricyclic β-lactams via intramolecular nitrilimine cycloaddition
No full textThe novel azeto[2',1':1,2]pyrrolo[3,4-c]pyrazole skeleton has been obtained in both racemic and enantiopure forms by means of intramol. cycloaddn. of nitrilimines. Fully stereoselective cycloaddns. were obtained, giving tricyclic b-lactams I (R = H, Me) as single diastereoisomers with good overall yields
1,3-Dipolar cycloadditions of MeOPEG-bounded azides
No full text1,3-Dipolar cycloadditions of MeOPEG-supported azide 2 with a variety of dipolarophiles have been studied. 1-MeOPEGsupported
1,2,3-triazoles 4 and 5, 1,2,3,4-tetrazoles 12 and aziridine 14 were obtained in nearly quantitative yields. The removal of the
MeOPEG moiety from the 1,2,3-triazole nucleus was achieved by acidic cleavage of the cycloadduct mixtures 4 and 5 giving 4- and 5-substituted-1,2,3-triazoles 6 and 7
Thieno[2,3-f]triazolo[1,5-a][1,4]diazepines and Thieno [2,3-f]triazolo[1,5-a][1,4]oxazepines from Azide Cycloaddition
No full textIntermolecular dipolar cycloadditions between 2-methoxycarbonyl-3-thenylazide (3) and monosubstituted dipolarophiles bearing a triple carbon-carbon bond were exploited in a three step synthesis of the title compounds. The intramolecular cycloaddition of substituted thenylazide (11) was also carried out in the two-step synthesis of the thieno[2,3-f][1,2,3]triazolo[1,5-a]-[1,4]diazepine derivative (8)
A bicyclo[3.1.1]heptano[4,3-c]pyrazole derived chiral auxiliary for dipolar cycloadditions
No full textStarting form naturally occurring (S)-cis-verbenol 1 and (1R)-( )-myrtenol 2, we synthesised enantiopure bicyclo[3.1.1]heptano[4,3-c]pyrazole derivatives 7 and 8 via a stereoselective nitrilimine cycloaddition as the key step. The effectiveness
of the above skeleton as a new chiral auxiliary was evaluated towards the 1,3-dipolar cycloadditions of nitrile oxides and nitrilimines.
Basic hydrolysis of the major cycloadducts gave enantiopure 5-carboxy-4,5-dihydroisoxazole (S)-(+)-19 and 5-carboxy-
4,5-dihydropyrazole (S)-(+)-20, respectively, which are of potential interest as chiral building blocks
A Short and Convenient Synthesis of Novel Thienopyrazolodiazepine and Thienopyrazoloxazepine Skeletons via Nitrilimine Cycloaddition
No full textSilver carbonate treatment of 3-thenyl-substituted hydrazonoyl chloride (3) promoted the in situ generation of the corresponding nitrilimine (4) which constitute the key intermediate in the three step synthesis of both thieno[2,3-f]pyrazolo[1,5-a][ 1,4]diazepine and thieno[2,3-f]pyrazolo[1,5-a][1, 4]-oxazepine skeletons. The concurrent formation of unusual pyridazine derivatives arising from the electrophilic attack of a nitrilium cation to the carbon-carbon double bond is also discussed in some detail
Nitrilimine cycloadditions to the cyano group in aqueous media
No full textDipolar cycloadditions between nitrilimines (2) and the cyano group
of activated nitriles (3) were exploited in aqueous sodium hydrogencarbonate as
reaction media in the presence of a surfactant. Short reaction times and mild
conditions were experienced affording 1-aryl-5-substituted 1,2,4-triazoles
A short synthesis of enantiopure 2-substituted 4,5-dihydro-1,4-benzodiazepin-3-ones via intramolecular azide cycloaddition
No full textStarting from the appropriate azides bearing the (S)-1-phenylethylamine and the l-alanine benzylester as chiral pendants, a facile and effective synthetic route to the title compounds in their enantiopure form was developed with excellent product yields obtained. Basic hydrolysis of the ester group of title compounds 3a–c gave the corresponding, readily functionalisable carboxylic acids. Catalytic reduction of 2-benzyl derivatives 3c and 3f gave 4-functionalised 1,2,4,5-tetrahydro-1,4-benzodiazepin-3-ones in enantiopure forms
Nitrilimine cycloaddition to 4-(pyrazol-5-yl)carbonyl-2-azetidinone and 4-(pyrazol-4-yl)carbonyl-2-azetidinone
No full textThe higly stereoselective nitrilimine cycloaddition onto the novel 3(R*)-phenyl-4(S*)-cinnamoyl-2-azetidinone 2 gave 4-(4,5-dihydropyrazol-5-yl)carbonyl-2-azetidinone 5 as the major product and 4-(4,5-dihydropyrazol-4-yl)carbonyl-2-azetidinone 6 as the minor one. Ceric ammonium nitrate (CAN) oxidation of the cycloadducts gave the title compounds with good overall yield. (C) 2003 Elsevier Science Ltd. All rights reserved
Reductive ring opening of 2-azetidinones promoted by sodium borohydride
No full textVariously substituted 2-azetidinones 3 and 4 were reacted with sodium borohydride in aqueous isopropanol giving 3-aminopropan-1,2-dioles 5 and 7. Reaction extent was dependent upon the substitution pattern in the 3- and 4-positions of the 2-azetidinone ring and revealed good correlation with carbonyl LUMO energies of starting 3. (c) 2006 Elsevier Ltd. All rights reserved
Nitrilimine cycloaddition onto 2-azetidinones bearing alkenyl dipolarophile(s)
No full textAbstract—Silver acetate-promoted nitrilimines cycloaddition onto 3(R*)-phenyl-4(R*)-cinnamoyl-2-azetidinone 1 were highly
stereoselective giving 4-(4,5-dihydropyrazol-5-yl) carbonyl-2-azetidinones 5 as the major products and regioisomeric 4-(4,5-
dihydropyrazol-4-yl) carbonyl-2-azetidinones 6 as the minor one. When the same protocol was applied to the novel 3(R*)-phenyl-4(S*)-
(4-benzoyl-E,E-1,3-butadienyl)-2-azetidinone 2 it resulted in site- and regioselective but not stereoselective cycloaddition, involving the
formation of the four cycloadducts 10–13
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