Thomas Lectka | |
---|---|
Born | |
Nationality | American |
Occupation(s) | Organic chemist, academic and researcher |
Title | Jean and Norman Scowe Professor of Chemistry |
Awards | NSF Career Award Camille Dreyfus Teacher-Scholar Award ACS Maryland Chemist of the Year |
Academic background | |
Education | B.A. in chemistry Ph.D. in organic chemistry |
Alma mater | Oberlin College Cornell University |
Academic work | |
Institutions | Johns Hopkins University |
Thomas Lectka is an American organic chemist,academic and researcher. He is Jean and Norman Scowe Professor of Chemistry and leads the Lectka Group at Johns Hopkins University. [1]
Lectka specializes in areas of catalysis in synthetic and mechanistic organic chemistry and has authored over 120 research publications. He has made contributions in the discovery of metal-catalyzed amide isomerization;the development of first practical method for the catalytic,asymmetric synthesis of beta-lactams;the synthesis of [C-F-C] fluoronium ions;and site-selective aliphatic fluorination. [2]
Lectka completed his bachelor's in chemistry and graduated from Oberlin College in 1985. He completed his doctoral degree in organic chemistry from Cornell University in 1991. He then completed his postdoctoral studies as an Alexander von Humboldt Postdoctoral Fellow at the University of Heidelberg in Germany and then as a National Institutes of Health Postdoctoral Fellow at Harvard University. [3]
Following his postdoctoral fellowship at Harvard University,Lectka joined Johns Hopkins University as an assistant professor of chemistry in 1994. He was promoted to associate professor in 1999 and to professor in 2002. In 2012,he was appointed as the Jean and Norman Scowe Professor of Chemistry at Johns Hopkins University. [4]
Lectka's research expertise lies in areas of catalysis in synthetic and mechanistic organic chemistry. He has contributed to the discovery of metal-catalyzed amide isomerization,and metal-catalyzed alkane fluorination,along with the development of first practical method for the catalytic,asymmetric synthesis of β-lactams.
During his studies at Cornell University from 1986 until 1991,Lectka focused on the design,synthesis,and study of stable carbocations with three-center,two-electron [C-H-C] bonds;and discussed the chemical shift of central hydrogen by the progressively smaller bond angles. [5] He also studied alkane protonolysis leading to stoichiometric hydrogen evolution, [6] MO theory of three-center bonding,and titanium promoted carbonyl coupling reactions. He investigated the reproducibility problems caused by the age,history and source of titanium chloride and introduced an optimized procedure that provided reproducibly high yields. [7] Lectka continued his research on MO theory and photoelectron spectroscopy during his fellowship at Heidelberg University. [8]
As a vellow at Harvard University,he focused on the asymmetric catalysis of the Diels-Alder reaction using bisoxazoline and bisimine Lewis acid complexes. After joining Johns Hopkins University in 1994,Lectka conducted research on new catalytic and asymmetric reactions,along with enantioselective reactions of imines,quinones and amides catalyzed by chiral Lewis acids [9] and nucleophiles;such as catalytic,asymmetric synthesis of β-lactams; [10] and nonnatural α- and β-amino acids. He presented the mechanism of the β-lactam development with proton sponge as the stoichiometric base,and also discussed the kinetic analysis of the catalyzed reaction of alkenes with α-imino esters. [11]
Lectka has studied the transition-metal catalyzed amide isomerization and peptide folding. [12] He presented the first spectroscopic and crystallographic proof of copper(II)-sodium coordination in tertiary amides and discussed the role of side chain in substituted prolines as a binding site for copper. [13] Lectka's research during his term at Johns Hopkins University also focused on enantioselective halogenation, [14] cooperative asymmetric catalysis,the medicinal chemistry of fluorinated molecules,and studies on asymmetric catalysis on sequentially-linked columns leading to synthesis machines. [15]
He conducted research on the chemistry of [C-F-C] fluoronium ions [16] and later reported first spectroscopic evidence for fluoronium ions in a solution. [17] Lectka has also worked on metal-catalyzed aliphatic fluorination [18] and site-selective aliphatic fluorination. [19]
Lectka has also established the use of fluorine as a through-space activating substituent for aromatic substitution. [20]
In organic chemistry,hydrocyanation is a process for conversion of alkenes to nitriles. The reaction involves the addition of hydrogen cyanide and requires a catalyst. This conversion is conducted on an industrial scale for the production of precursors to nylon.
In organic chemistry,the Ugi reaction is a multi-component reaction involving a ketone or aldehyde,an amine,an isocyanide and a carboxylic acid to form a bis-amide. The reaction is named after Ivar Karl Ugi,who first reported this reaction in 1959.
The Corey–Itsuno reduction,also known as the Corey–Bakshi–Shibata (CBS) reduction,is a chemical reaction in which a prochiral ketone is enantioselectively reduced to produce the corresponding chiral,non-racemic alcohol. The oxazaborolidine reagent which mediates the enantioselective reduction of ketones was previously developed by the laboratory of Itsuno and thus this transformation may more properly be called the Itsuno-Corey oxazaborolidine reduction.
In chemistry,transfer hydrogenation is a chemical reaction involving the addition of hydrogen to a compound from a source other than molecular H2. It is applied in laboratory and industrial organic synthesis to saturate organic compounds and reduce ketones to alcohols,and imines to amines. It avoids the need for high-pressure molecular H2 used in conventional hydrogenation. Transfer hydrogenation usually occurs at mild temperature and pressure conditions using organic or organometallic catalysts,many of which are chiral,allowing efficient asymmetric synthesis. It uses hydrogen donor compounds such as formic acid,isopropanol or dihydroanthracene,dehydrogenating them to CO2,acetone,or anthracene respectively. Often,the donor molecules also function as solvents for the reaction. A large scale application of transfer hydrogenation is coal liquefaction using "donor solvents" such as tetralin.
Danishefsky's diene is an organosilicon compound and a diene with the formal name trans-1-methoxy-3-trimethylsilyloxy-buta-1,3-diene named after Samuel J. Danishefsky. Because the diene is very electron-rich it is a very reactive reagent in Diels-Alder reactions. This diene reacts rapidly with electrophilic alkenes,such as maleic anhydride. The methoxy group promotes highly regioselective additions. The diene is known to react with amines,aldehydes,alkenes and alkynes. Reactions with imines and nitro-olefins have been reported.
In organic chemistry,organocatalysis is a form of catalysis in which the rate of a chemical reaction is increased by an organic catalyst. This "organocatalyst" consists of carbon,hydrogen,sulfur and other nonmetal elements found in organic compounds. Because of their similarity in composition and description,they are often mistaken as a misnomer for enzymes due to their comparable effects on reaction rates and forms of catalysis involved.
The Hajos–Parrish–Eder–Sauer–Wiechert and Barbas-List reactions in organic chemistry are a family of proline-catalysed asymmetric aldol reactions.
Bis(oxazoline) ligands (often abbreviated BOX ligands) are a class of privileged chiral ligands containing two oxazoline rings. They are typically C2‑symmetric and exist in a wide variety of forms;with structures based around CH2 or pyridine linkers being particularly common (often generalised BOX and PyBOX respectively). The coordination complexes of bis(oxazoline) ligands are used in asymmetric catalysis. These ligands are examples of C2-symmetric ligands.
The Staudinger synthesis,also called the Staudinger ketene-imine cycloaddition,is a chemical synthesis in which an imine 1 reacts with a ketene 2 through a non-photochemical 2+2 cycloaddition to produce a β-lactam3. The reaction carries particular importance in the synthesis of β-lactam antibiotics. The Staudinger synthesis should not be confused with the Staudinger reaction,a phosphine or phosphite reaction used to reduce azides to amines.
DuPhos is a class of organophosphorus compound that are used ligands for asymmetric synthesis. The name DuPhos is derived from (1) the chemical company that sponsored the research leading to this ligand's invention,DuPont and (2) the compound is a diphosphine ligand type. Specifically it is classified as a C2-symmetric ligand,consisting of two phospholanes rings affixed to a benzene ring.
Lectka and co-workers developed a catalytic,asymmetric method to synthesize β-lactams.
A Josiphos ligand is a type of chiral diphosphine which has been modified to be substrate-specific;they are widely used for enantioselective synthesis. They are widely used in asymmetric catalysis.
In Lewis acid catalysis of organic reactions,a metal-based Lewis acid acts as an electron pair acceptor to increase the reactivity of a substrate. Common Lewis acid catalysts are based on main group metals such as aluminum,boron,silicon,and tin,as well as many early and late d-block metals. The metal atom forms an adduct with a lone-pair bearing electronegative atom in the substrate,such as oxygen,nitrogen,sulfur,and halogens. The complexation has partial charge-transfer character and makes the lone-pair donor effectively more electronegative,activating the substrate toward nucleophilic attack,heterolytic bond cleavage,or cycloaddition with 1,3-dienes and 1,3-dipoles.
Hydrogen-bond catalysis is a type of organocatalysis that relies on use of hydrogen bonding interactions to accelerate and control organic reactions. In biological systems,hydrogen bonding plays a key role in many enzymatic reactions,both in orienting the substrate molecules and lowering barriers to reaction. The field is relatively undeveloped compared to research in Lewis acid catalysis.
Radical fluorination is a type of fluorination reaction,complementary to nucleophilic and electrophilic approaches. It involves the reaction of an independently generated carbon-centered radical with an atomic fluorine source and yields an organofluorine compound.
In organic chemistry,the Roskamp reaction is a name reaction describing the reaction between α-diazoesters (such as ethyl diazoacetate) and aldehydes to form β-ketoesters,often utilizing various Lewis acids (such as BF3,SnCl2,and GeCl2) as catalysts. The reaction is notable for its mild reaction conditions and selectivity.
Iwao Ojima is a Japanese-American chemist and university distinguished professor at the State University of New York at Stony Brook. He has been widely recognized for his seminal contributions to a range of chemical research at the multifaceted interfaces of chemical synthesis and life sciences. As rare accomplishments,he has received four National Awards from the American Chemical Society in four different fields of research. He is also serving as the director of the Institute of Chemical Biology and Drug Discovery (ICB&DD),as well as the president of the Stony Brook Chapter of the National Academy of Inventors.
The nitro-Mannich reaction is the nucleophilic addition of a nitroalkane to an imine,resulting in the formation of a beta-nitroamine. With the reaction involving the addition of an acidic carbon nucleophile to a carbon-heteroatom double bond,the nitro-Mannich reaction is related to some of the most fundamental carbon-carbon bond forming reactions in organic chemistry,including the aldol reaction,Henry reaction and Mannich reaction.
The ketimine Mannich reaction is an asymmetric synthetic technique using differences in starting material to push a Mannich reaction to create an enantiomeric product with steric and electronic effects,through the creation of a ketimine group. Typically,this is done with a reaction with proline or another nitrogen-containing heterocycle,which control chirality with that of the catalyst. This has been theorized to be caused by the restriction of undesired (E)-isomer by preventing the ketone from accessing non-reactive tautomers. Generally,a Mannich reaction is the combination of an amine,a ketone with a β-acidic proton and aldehyde to create a condensed product in a β-addition to the ketone. This occurs through an attack on the ketone with a suitable catalytic-amine unto its electron-starved carbon,from which an imine is created. This then undergoes electrophilic addition with a compound containing an acidic proton. It is theoretically possible for either of the carbonyl-containing molecules to create diastereomers,but with the addition of catalysts which restrict addition as of the enamine creation,it is possible to extract a single product with limited purification steps and in some cases as reported by List et al.;practical one-pot syntheses are possible. The process of selecting a carbonyl-group gives the reaction a direct versus indirect distinction,wherein the latter case represents pre-formed products restricting the reaction's pathway and the other does not. Ketimines selects a reaction group,and circumvent a requirement for indirect pathways.
Mono-N-protected amino acid (MPAA) is a bifunctional ligand that plays a key role in C–H functionalizations by accelerating the reaction rate and imparting specified chirality into the product. Amino acids are ideal building blocks for chiral ligand synthesis due to the cost,accessibility,large variety,solubility,and inherent chirality. Naturally occurring amino acids are transformed into chiral MPAA ligands that,upon coordination to metal complexes,allow reactions to occur that are otherwise energetically unfavorable. Great strides in the development of MPAA ligands over the past two decades have led to the integral role that enantioselective catalysis now plays in complex organic synthesis.
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