As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile. Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions. Typical non-nucleophilic bases are bulky, such that protons can attach to the basic center but alkylation and complexation is inhibited.
A variety of amines and nitrogen heterocycles are useful bases of moderate strength (pKa of conjugate acid around 10-13)
Non-nucleophilic bases of high strength are usually anions. For these species, the pKas of the conjugate acids are around 35–40.
Other strong non-nucleophilic bases are sodium hydride and potassium hydride. These compounds are dense, salt-like materials that are insoluble and operate by surface reactions.
Some reagents are of high basicity (pKa of conjugate acid around 17) but of modest but not negligible nucleophilicity. Examples include sodium tert-butoxide and potassium tert-butoxide.
The following diagram shows how the hindered base, lithium diisopropylamide, is used to deprotonate an ester to give the enolate in the Claisen ester condensation, instead of undergoing a nucleophilic substitution.
This reaction (deprotonation with LDA) is commonly used to generate enolates.
In organic chemistry, a ketone is a functional group with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.
An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties react to form a β-hydroxyaldehyde or β-hydroxyketone, and this is then followed by dehydration to give a conjugated enone.
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionic. Owing to the polar nature of the C−Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
Lithium diisopropylamide is a chemical compound with the molecular formula LiN(CH 2)2. It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature. It is a colorless solid, but is usually generated and observed only in solution. It was first prepared by Hamell and Levine in 1950 along with several other hindered lithium diorganylamides to effect the deprotonation of esters at the α position without attack of the carbonyl group.
In organic chemistry, enolates are organic anions derived from the deprotonation of carbonyl compounds. Rarely isolated, they are widely used as reagents in the synthesis of organic compounds.
The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base. The reaction produces a β-keto ester or a β-diketone. It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1887. The reaction has often been displaced by diketene-based chemistry, which affords acetoacetic esters.
n-Butyllithium C4H9Li (abbreviated n-BuLi) is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene (SBS). Also, it is broadly employed as a strong base (superbase) in the synthesis of organic compounds as in the pharmaceutical industry.
A superbase is a compound that has a particularly high affinity for protons. Superbases are of theoretical interest and potentially valuable in organic synthesis. Superbases have been described and used since the 1850s.
N,N-Diisopropylethylamine, or Hünig's base, is an organic compound that is a tertiary amine. It is named after the German chemist Siegfried Hünig. It is used in organic chemistry as a non-nucleophilic base. It is commonly abbreviated as DIPEA,DIEA, or i-Pr2NEt.
In stereochemistry, a chiral auxiliary is a stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis. The chirality present in the auxiliary can bias the stereoselectivity of one or more subsequent reactions. The auxiliary can then be typically recovered for future use.
Potassium tert-butoxide (or potassium t-butoxide) is a chemical compound with the formula [(CH3)3COK]n (abbr. KOtBu). This colourless solid is a strong base (pKa of conjugate acid around 17), which is useful in organic synthesis. The compound is often depicted as a salt, and it often behaves as such, but its ionization depends on the solvent.
The Weinreb–Nahm ketone synthesis is a chemical reaction used in organic chemistry to make carbon–carbon bonds. It was discovered in 1981 by Steven M. Weinreb and Steven Nahm as a method to synthesize ketones. The original reaction involved two subsequent nucleophilic acyl substitutions: the conversion of an acid chloride with N,O-Dimethylhydroxylamine, to form a Weinreb–Nahm amide, and subsequent treatment of this species with an organometallic reagent such as a Grignard reagent or organolithium reagent. Nahm and Weinreb also reported the synthesis of aldehydes by reduction of the amide with an excess of lithium aluminum hydride.
Diisopropylamine is a secondary amine with the chemical formula (Me2CH)2NH (Me = methyl). Diisopropylamine is a colorless liquid with an ammonia-like odor. Its lithium derivative, lithium diisopropylamide, known as LDA is a widely used reagent.
Phosphazenes refer to classes of organophosphorus compounds featuring phosphorus(V) with a double bond between P and N. One class of phosphazenes have the formula R−N=P(−NR2)3. These phosphazenes are also known as iminophosphoranes and phosphine imides. They are superbases. Another class of compounds called phosphazenes are represented with the formula (−N=P 2−)n, where X = halogen, alkoxy group, amide and other organyl groups. One example is hexachlorocyclotriphosphazene (−N=P 2−)3. Bis(triphenylphosphine)iminium chloride [Ph3P=N=PPh3]+Cl−is also referred to as a phosphazene, where Ph = phenyl group. This article focuses on those phosphazenes with the formula R−N=P(−NR2)3.
Wender Taxol total synthesis in organic chemistry describes a Taxol total synthesis by the group of Paul Wender at Stanford University published in 1997. This synthesis has much in common with the Holton Taxol total synthesis in that it is a linear synthesis starting from a naturally occurring compound with ring construction in the order A,B,C,D. The Wender effort is shorter by approximately 10 steps.
Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula LiN(Si(CH3)3)2. It is commonly abbreviated as LiHMDS or Li(HMDS) (lithium hexamethyldisilazide - a reference to its conjugate acid HMDS) and is primarily used as a strong non-nucleophilic base and as a ligand. Like many lithium reagents, it has a tendency to aggregate and will form a cyclic trimer in the absence of coordinating species.
Organosodium chemistry is the chemistry of organometallic compounds containing a carbon to sodium chemical bond. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are commercially available and exhibit more convenient reactivity.
Sodium tert-butoxide (or sodium t-butoxide) is a chemical compound with the formula (CH3)3CONa (abbr. NaOtBu). It is a strong, non-nucleophilic base. It is flammable and moisture sensitive. It is sometimes written in the chemical literature as sodium t-butoxide. It is similar in reactivity to the more common potassium tert-butoxide.
Alpha-substitution reactions occur at the position next to the carbonyl group, the α-position, and involve the substitution of an α hydrogen atom by an electrophile, E, through either an enol or enolate ion intermediate.
P4-t-Bu is a readily accessible chemical from the group of neutral, peralkylated sterically hindered polyaminophosphazenes, which are extremely strong bases but very weak nucleophiles, with the formula (CH3)3C−N=P(−N=P(−N(CH3)2)3)3. "t-Bu" stands for tert-butyl(CH3)3C–. "P4" stands for the fact that this molecule has 4 phosphorus atoms. P4-t-Bu can also be regarded as tetrameric triaminoiminophosphorane of the basic structure H−N=P(−NH2)3. The homologous series of P1 to P7 polyaminophosphazenes of the general formula with preferably methyl groups as R1, a methyl group or tert-butyl group as and even-numbered x between 0 and 6 (P4-t-Bu: R1 = Me, R2 = t-Bu and x = 3) has been developed by Reinhard Schwesinger; the resulting phosphazene bases are therefore also referred to as Schwesinger superbases.
