151775-20-1Relevant articles and documents
(S)-(?)-Fluorenylethylchloroformate (FLEC); preparation using asymmetric transfer hydrogenation and application to the analysis and resolution of amines
Amin, Mohammad A.,Camerino, Michelle A.,Mountford, Simon J.,Ma, Xiao,Manallack, David T.,Chalmers, David K.,Wills, Martin,Thompson, Philip E.
, (2019/09/19)
Fluorenylethylchoroformate (FLEC) is a valuable chiral derivatisation reagent that is used for the resolution of a wide variety of chiral amines. Herein, we describe an improved preparation of (S)-(?)-FLEC using an efficient asymmetric catalytic transfer hydrogenation as the key step. We also demonstrate the application of FLEC as a chiral Fmoc equivalent for chiral resolution, with facile deprotection, of tetrahydroquinaldines, and its capacity for inducing regioselective outcomes in nitration reactions.
First chemoenzymatic synthesis of (R)- and (S)-1-(9H-fluoren-9-yl)ethanol
Borowiecki, Pawel,Balter, Sylwia,Justyniak, Iwona,Ochal, Zbigniew
, p. 1120 - 1126 (2013/10/08)
A simple chemoenzymatic synthesis of 1-(9H-fluoren-9-yl)ethanol stereoisomers is described. The enantiomers were resolved by a kinetically controlled transesterification with vinyl acetate in the presence of commercially available lipases. High-throughput screening and subsequent exhaustive investigation of the utility of the lipases in a stereoselective process of introducing chirality have been carried out. Lipase A from Candida antarctica as a cross-linked aggregate (CAL-A-CLEA) was the most efficient enzyme for the resolution of the title compound providing (S)-1-(9H-fluoren-9- yl)ethanol and its (R)-acetate in enantiopure form (>99% ee). Under mild reaction conditions, excellent enantioselectivity (E = 407), and good isolated yields of the products were obtained.
(+)-Fluorenylethylchloroformate (FLEC)-improved synthesis for application in chiral analysis and peptidomimetic synthesis
Camerino, Michelle A.,Chalmers, David K.,Thompson, Philip E.
, p. 2571 - 2573 (2013/06/05)
An efficient synthesis of the enantiomers of fluorenylethylchloroformate (FLEC) has been achieved that allows the routine application of the reagent for the resolution of chiral amines including unusual amino acids. The utility of the fluorenylethoxycarbonyl (Feoc) group as a chiral Fmoc equivalent, for combined resolution and protection of amino acids, in solid phase peptide synthesis is also shown.
Synthesis of chiral alcohols by asymmetric reductions of various ketones including α-aminophenones
Brown, Eric,Leze, Antoine,Touet, Joel
, p. 2029 - 2040 (2007/10/03)
LiAlH4 previously treated with 2.5 equiv. of (S)-(+) or (R)-(-)-2-(2-isoindolinyl)butan-1-ol 1 reduced the six α-aminophenones 4-9 into the corresponding optically active β-aminoalcohols 10-15 whose ee's were in the range of 40-97% after chroma
Solvent-promoted E2 reaction competing with SN2 reaction and stepwise solvolytic elimination and substitution reactions
Meng, Qingshui,Thibblin, Alf
, p. 9399 - 9407 (2007/10/03)
Solvolysis of 9-(1-X-ethyl)fluorene (1-X, X = I, Br, Cl, OTs, or OBs) in 25 vol % acetonitrile in water gives the elimination products 9-(1-ethylidene)fluorene (3) and 9-vinylfluorene (2) and the substitution products 9-(1-hydroxyethyl)fluorene (1-OH) and
Laser flash photolysis of 9-diazofluorene in low-temperature glasses
Ruzicka, Jan,Leyva, Elisa,Platz, Matthew S.
, p. 897 - 905 (2007/10/02)
The laser flash photolysis of 9-diazofluorene was investigated in several viscous organic glasses at low temperature. The data indicate that triplet fluorenylidene reacts with "soft warm" glasses by classical H atom abstraction, but the mechanism changes to quantum mechanical tunneling in colder and more rigid matrices.
N-S Cleavage Is Faster Than Homolytic Ring Opening in Single-Electron Transfer to Some N-Sulfonylaziridines. Competition between SN2 and SET
Bellos, Konstantinos,Stamm, Helmut,Speth, Dieter
, p. 6846 - 6849 (2007/10/02)
The radical anions of the N-sulfonylaziridines, 1a,b and 3 undergo N-S cleavage in place of homolytic ring opening as is demonstrated by reactions with anthracenide A*-.Nucleophilic ring opening of the sulfonylaziridines 1a,b and 3 by the carbanions AH-, X-, and Fl- of dihydroanthracene, xanthene, and fluorene, respectively, proceeds with the expected regioselectivity and is slow enough to allow some competition by a single-electron transfer (SET) initiated N-S cleavage, which provides the desulfonated aziridines and bixanthenyl X-X or bifluorenyl Fl-Fl, respectively.The SET path is favored by light.The competition is in favor of SET to the exclusion of the nucleophilic opening when trityl anion reacts with 1a.The twice-found byproducts 11 and 12 require the azirine intermediate 15, which is, at least formally, generated by elimination of TsH from 1a in a non-SET reaction.
Separation of Amino Acid Enantiomers and Chiral Amines Using Precolumn Derivatization with (+)-1-(9-Fluorenyl)ethyl Chloroformate and Reversed-Phase Liquid Chromatography
Einarsson, Stefan,Josefsson, Bjoern,Moeller, Per,Sanchez, Domingo
, p. 1191 - 1195 (2007/10/02)
A new chiral reagent (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC) was synthesized for separation of amino acid enentiomers and optically active amines.Highly fluorescent diastereomers of amino acids were obtained without racemization within 4 min at room temperature.The derivatives have favorable chromatographic properties, which is demonstrated by a reversed-phase separation of the D and L form of 17 primary amino acids in a single run.The secondary amino acids were resolved separately at a lower pH and can be determined without interferences from primary amino acids.The stability of the derivatives permitted confirmation studies with gas chromatography-mass spectrometry.
Reinvestigation of the Chemistry of Arylcarbenes in Polycrystalline Alcohols at 77 K. Secondary Photochemistry of Matrix-Isolated Carbenes
Leyva, Elisa,Barcus, Robert L.,Platz, Matthew S.
, p. 7786 - 7788 (2007/10/02)
Photolysis of diphenyldiazomethane (DPDM) in frozen alcoholic matrices gives ground-state triplet diphenylcarbene (DPC).At 77 K 3DPC reacts primarily with alcohols by OH insertion to give ethers.Photolysis of 3DPC produces an excited carbene 3DPC* which reacts with the matrix by H-atom abstraction to ultimately give alcohol-type products.Secondary photolysis of triplet fluorenylidene at 77 K is not as prevalent as that of 3DPC.
Studies of the Borderline between Concerted and Stepwise Mechanisms of Elimination : E1cB Elimination of Fluoren-9-ylmethyl Carboxylate Esters
O'Ferrall, Rory A. More,Larkin, Finbar,Walsh, Peter
, p. 1573 - 1580 (2007/10/02)
Rates of β-elimination of carboxylate leaving groups from fluoren-9-ylmethyl carboxylate esters in methanolic sodium methoxide at 25 deg C are reported.An E1cB mechanism with rate-determining formation of a carbanion intermediate is assigned on the basis of near identity of measured elimination rates and rates of carbanion formation predicted from a Taft correlation, and the similarity with elimination of 1-(1-acetoxy-1-methylethyl)indene for which the mechanism has been established by Ahlberg and Thibblin.Values of ρ=0.42 and βlg=0.27 measured for substituted benzoate leaving groups are a little larger than expected (ca. 0.24 and 0.18, respectively) and the discrepancy is tentatively ascribed to conformational enhancement of remote substituent effects, rather than to a contribution of E2 elimination.The effects of alkyl and aryl substitution α to the leaving group are discussed, especially in relation to the borderline between concerted and stepwise mechanisms.The measurements fail to confirm an earlier inference that the borderline shows a discontinuity in transition-state structure at the point of mechanistic change.
