53692-73-2Relevant academic research and scientific papers
1-[(E)-2-arylethenyl]-2,2-diphenylcyclopropanes: Kinetics and mechanism of rearrangement to cyclopentenes
Mulzer, Johann,Huisgen, Rolf,Arion, Vladimir,Sustmann, Reiner
experimental part, p. 1359 - 1388 (2011/10/09)
Kinetic measurements for the thermal rearrangement of 2,2-diphenyl-1-[(E)- styryl]cyclopropane (22a) to 3,4,4-triphenylcyclopent-1-ene (23a) in decalin furnished ΔHρm{{-{isom}^{ne }}}$=31.0±1.2kcal mol-1 and ΔSρm{{-{isom}^{ne }}}$=-6. 0±2.6e.u. The lowering of ΔHa‰ by 20kcal mol-1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (+)-(S)-22a proceeds with ΔHρm{{-{rac}^{ne }}}$=28.2±0.8kcal mol -1 and ΔSρm{{-{rac}^{ne }}}$=-5±2e.u., and is at 150° 106 times faster than the rearrangement. Seven further 1-(2-arylethenyl)-2,2-diphenylcyclopropanes 22, (E)- and (Z)-isomers, were synthesized and characterized. The (E)-compounds showed only modest substituent influence in their krac (at 119.4°) and kisom (at 159.3°) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log krac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring-opening of the preponderant s-trans-conformation of 22 gives rise to the 1-exo-phenylallyl radical 26 that bears the diphenylethyl radical in 3-exo-position, and is responsible for racemization. The 1-exo-3-endo-substituted allylic diradical 27 arises from the minor s-gauche-conformation of 22 and is capable of closing the three- or the five-membered ring, 22 or 23, respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum-chemical calculations by Houk etal. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate? Copyright
Electronically tuned chiral ruthenium porphyrins: Extremely stable and selective catalysts for asymmetric epoxidation and cyclopropanation
Berkessel, Albrecht,Kaiser, Patrick,Lex, Johann
, p. 4746 - 4756 (2007/10/03)
We report the use of three enantiomerically pure and electronically tuned ruthenium carbonyl porphyrin catalysts for the asymmetric cyclopropanation and epoxidation of a variety of olefinic substrates. The D4-symmetric ligands carry a methoxy, a methyl or a trifluoromethyl group at the 10-position of each of the 9-[anti-(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene)]-substituents at the meso-positions of the porphyrin. Introduction of a CF 3-substituent in this remote position resulted in greatly improved catalyst stability, and turnover numbers of up to 7500 were achieved for cyclopropanation, and up to 14200 for epoxidation, with ee values typically >90% and ≈80%, respectively. In one example, the axial CO ligand at the ruthenium was exchanged for PF3, resulting in the first chiral ruthenium porphyrin with a PF3 ligand reported to date. In cyclopropanations with ethyl diazoacetate, the latter catalyst performed exceedingly well, and gave a 95% ee in the case of 1,1-diphenylethylene as substrate.
2,2′-isopropylidenebis[(4R)-(1-adamantyl)-2-oxazoline] (Adam-Box). A new enantiopure C2-symmetrical ligand: Enantioselective cyclopropanations, Diels-Alder reactions, and allylic oxidations
Clariana, Jaume,Comelles, Josep,Moreno-Maas, Marcial,Vallribera, Adelina
, p. 1551 - 1554 (2007/10/03)
The title bisoxazoline (Box) featuring two adamantane skeletons (Adam-Box) is a ligand of (R,R)-configuration, which combined with copper sources makes excellent catalysts for enantioselective cyclopropanations, Diels-Alder reactions, and allylic oxidations.
Enantioselective Cyclopropanation of 1,1-Diphenylethylene and Diazoacetic Acid Ester with Copper Catalysts
Brunner, Henri,Miehling, Wolfgang
, p. 1237 - 1254 (2007/10/02)
Copper(II) compounds catalyze the reaction of 1,1-diphenylethylene with diazoacetic acid ethylester.The main product is 2,2-diphenylcyclopropane carboxylic acid ethylester.The formation of the carbene dimerization products fumaric and maleic acid diethylester can be suppressed by the continuous addition of diazoacetic ester to 1,1-diphenylethylene. 37 optically active ligands, partly new, were combined with copper(II)-acetate to give in-situ-catalysts.In five cases isolated copper complexes were used as catalysts.The best optical inductions in the formation of 2,2-diphenylcyclopropane carboxylic acid ethylester with up to 65.6percent ee were achived with Schiffbase ligands, which derive from salicylaldehyde and amino alcohols, obtained from amino acid esters and phenyl Grignard. - Keywords: Catalytic enantioselective cyclopropanation; Copper(II) catalysts; Optical induction.
