Search results for "arrangement."
showing 10 items of 343 documents
Photochemical ligand rearrangement in dirhodium(II) compounds. Structure of Rh2(O2CCH3)2(η2-O2CCH3)[(C6H4)PPh2] (η2-PCCl)(PCClP-ClC6H4)Ph2
1995
Abstract The photochemical reaction of the adducts Rh2(O2CCH3)3[(C6H4)P(o-ClC6H4)Ph]· (P(p-XC6H4)3) (X=H, Me, Cl), yield the compounds Rh2(O2CCH3)2(η2-O2CCH3)[(p-XC6H3)P (p-XC6H4)2](η2-PCCl), (PCCl=P(o-ClC6H4)Ph2) in a ligand rearrangement reaction that involves activation of CH and RhC bonds. The factors that favour this process are studied by carrying out photochemical reactions with different phosphines. The structures of Rh2(O2CCH3)2(η2-O2CCH3) [(C6H4)PPh2](η2-PCCl) has been determined by X-ray diffraction. Mr=1321.1, orthorhombic, space group Pbcn, a=20.339(8), b=20.07(6), c=23.07(3) A , V=9413(3) A 3 , Z=8, D x =1.86 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.071…
Selective favorskii rearrangement in macrocyclic rings
1981
Abstract A mixture of 2,2-dibromo-12-chlorocyclododecanone (IIa) and 2,12-dibromo-2-chlorocyclododecanone (IIb) by Favorskii rearrangement gave selectively methyl 2-chloro-1-cycloundecene-1-carboxylate (IIIa).
Solution-, solid-phase, and fluorous synthesis of beta,beta-difluorinated cyclic quaternary alpha-amino acid derivatives: a comparative study.
2008
The diastereoselective synthesis of cyclic beta,beta-difluorinated alpha-amino acid derivatives bearing a quaternary stereocenter is described. The process relies on the chemo- and diastereoselective addition of allylic organometallic reagents to fluorinated alpha-imino esters and a subsequent ring-closing metathesis reaction (RCM). Complete selectivity in the nucleophilic addition was achieved with (R)-phenylglycinol methyl ether as a chiral auxiliary. The resulting amino acids were introduced into peptide chains, which could facilitate the preparation of potentially bioactive dipeptide derivatives. In addition, the solution synthesis of these cyclic fluorinated alpha-amino acids was succe…
Chemical Modification of Calix[4]arenes and Resorcarenes
2001
Aza-Claisen Rearrangement
2007
ChemInform Abstract: A New Palladium(II)-Catalyzed [3,3] Aza-Claisen Rearrangement of 3-Allyloxy-5-aryl-1,2,4-oxadiazoles.
2011
Substituted derivatives such as (Ib,c) react with very high degree of stereochemistry explained by a cationic palladacycle intermediate similar to the one postulated for the Cope-rearrangement of 1,5-dienes.
ChemInform Abstract: First Synthesis of Medium-Sized Ring Allenyl Lactams.
2012
Medium-sized lactams bearing an axially chiral allene unit have been synthesized by using an aza-ketene Claisen rearrangement. Starting from 2-alkynylpiperidines or 2-alkynylazepines, ring enlargement enabled the highly diastereoselective formation of 10- or 11-membered lactams with a 4,5-allene subunit. X-ray analysis of the allenylacezinone showed the presence of a strained cumulated olefin system with a defined arrangement of the functional groups. The cyclic allenes were found to be stable upon heating up to 50 °C.
First Synthesis of Medium-Sized Ring Allenyl Lactams
2011
Medium-sized lactams bearing an axially chiral allene unit have been synthesized by using an aza-ketene Claisen rearrangement. Starting from 2-alkynylpiperidines or 2-alkynylazepines, ring enlargement enabled the highly diastereoselective formation of 10- or 11-membered lactams with a 4,5-allene subunit. X-ray analysis of the allenylacezinone showed the presence of a strained cumulated olefin system with a defined arrangement of the functional groups. The cyclic allenes were found to be stable upon heating up to 50 °C.
Structure Effect of Imidazolium-Based Dicationic Ionic Liquids on Claisen Rearrangement
2014
A large group of imidazolium-based dicationic ionic liquids (DILs) has been prepared in good yields. Thermal stability of all DILs has been determined. The effects of the reaction time, cation, imidazolium C2–H acidity, and anion on the Claisen rearrangement of allyl phenyl ether have been investigated. Type of anion and the presence of the acidic C2–H bond in the imidazolium moieties have proven to be essential for this reaction. The simple procedure and the possibility of avoiding the use catalysts and volatile organic solvents make this synthetic method environmentally benign and adaptable for large-scale applications.