1,721,011 research outputs found
MeOPEG-bounded azide cycloadditions to alkynyl dipolarophiles
No full textThe MeOPEG-supported azide 2 was reacted in the presence of a number of alkynyl dipolarophiles. The corresponding 1-MeOPEG-supported-1,2,3-triazoles were obtained in nearly quantitative yields. Acidic hydrolysis of the cycloadducts 5b and 6b caused the removal of the MeOPEG pendant giving 4-methoxycarbonyl-1,2,3-triazole 9 and 5-methoxycarbonyl-1,2,3-triazole 10, respectively. (C) 2003 Elsevier Science Ltd. All rights reserved
Behavior of hydrazonoyl chlorides towards the C=N double bond of Delta(2)-pyrazolines. A study on 2-(4-nitrophenyl)-2,3,3a,4,5,6-hexahydro-6-oxofuro[3,4-c]pyrazole
No full textThe reaction between title compound (3) and hydrazonoyl chlorides (4) was performed in the presence of triethylamine or silver salts. The product output was quite different depending upon the basic agent and, besides the formation of the novel pyrazolo[4,5-b]furo[3,4-c]pyrazole skeleton, a new degradative behavior of the pyrazoline ring has been observed
On some Derivatives of 2-Hydroxyglutaric Acid
No full textS- and R-acetoxyglutaric acid dimethyl esters are synthesized starting from S and R glutamic acids. Specific optical rotation values given in the literature for some derivatives of 5-oxo-2-S-tetrahydrofuronic acid, an intermediate in the above synthesis, are corrected
Oxygenated monoterpenes as dipolarophiles for nitrilimine cycloadditions
No full textA variety of naturally-occurring oxygenated monoterpenes, namely (S)-cis-verbenol, (1R)-(-)-myternol, (1S)-(-)-verbenone, (1R)-(-)-myternal, (S)-(-)-perillyl alcohol, and (S)-(-)-perillaldehyde have been submitted to nitrilimine cycloaddition. These processes were fully regio- and stereoselective for four dipolarophiles. In contrast, regioselective but non-stereoselective cycloadditions occurred in the case of two of the monoterpene derivatives. The configurations of the newly-formed stereocentres of the cycloadducts were assigned on the basis of NOE and NOESY experiments
Nitrilimine cycloadditions to MeOPEG-bounded alkenyl dipolarophiles
No full textBase treatment of hydrazonoyl chloride 2 with MeOPEG-supported acrylates 1 and acrylamides 5 gave the corresponding MeOPEG-supported 4,5-dihydropyrazoles 3 and 6. Basic hydrolysis of the cycloadducts caused the removal of the MeOPEG pendant giving 5-carboxy- or 5-aminocarbonyl- 4,5-dihydropyrazoles 7 and 8, respectively. Cycloaddition between 2 and enantiopure MeOPEG-supported acrylamide 10 gave a mixture of MeOPEG-supported cycloadducts 11 and 12 with low diastereoselectivity
Synthesis of Bis-(3,5)pyrazolophanes by Sequential Intermolecular-Intramolecular Nitrilimine Cycloadditions
No full textA series of bis-(3,5)pyrazolophanes of potential interest in supramolecular chemistry have been synthesized by exploiting sequential intermolecular-intramolecular cycloadditions of properly functionalised nitrilimines. (C) 1998 Elsevier Science Ltd. All rights reserved
SILVER CARBONATE PROMOTED REACTION OF HYDRAZONYL CHLORIDES WITH ALLYLIC ALCOHOLS
No full textThe title reaction affords two main kinds of products: (i) pyrazole derivatives due to cycloaddition of a nitrile imine intermediate to the ethylenic bond; (ii) open-chain carbonyl compounds due to the electrophilic attack of a nitrilium-like carbocation to the ethylenic bond. Mechanistic possibilities are discussed
SYNTHESIS OF [1,2,3]TRIAZOLO[1,5-A][4,1]BENZOXAZEPINE VIA INTRAMOLECULAR AZIDE CYCLOADDITION
No full textStarting from isatoic anhydride and propargyl alcohols, we developed a synthetic approach to the title compounds, where the key step is an intramolecular cycloaddition of the azido group onto the acetylenic bond
Diastereoselective cycloadditions of nitrilimines to enantiopure acrylamides
No full textThe diastereoselective cycloaddition of the nitrilimine 2 with enantiopure acrylamides 3 was exploited to obtain enantiopure 4,5-dihydropyrazoles 4 and 5. Basic hydrolysis of the cycloadducts gave the dicarboxy derivatives 6 and 7 or 8 and 9, which are of potential interest as new chiral building blocks. (C) 2002 Elsevier Science Ltd. All rights reserved
NOVEL-APPROACH TO 1-ARYL-1H-4,1,2-BENZOXADIAZINES INVOLVING A SMILES REARRANGEMENT
No full textSome representatives of the title ring system have been obtained from ortho-(aryloxy)phenylhydrazonyl chlorides through a pathway involving (i) nitrile imide formation, (ii) Smiles rearrangement and (iii) intramolecular nucleophilic addition
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