Montréalone (synonyms: montrealone, phospha-münchnone) is a

mesoionic In chemistry, mesoionic compounds are one in which a heterocyclic structure is dipolar and where both the negative and the positive charges are delocalized. A completely uncharged structure cannot be written and mesoionic compounds cannot be repr ...

heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

. It is named for the city of

Montréal Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in Canada by population, second-largest in Canada, and the List of North American cit ...

, Canada, which is the location of

McGill University McGill University (French: Université McGill) is an English-language public research university in Montreal, Quebec, Canada. Founded in 1821 by royal charter,Frost, Stanley Brice. ''McGill University, Vol. I. For the Advancement of Learning, ...

, where it was first discovered.

Structure

The montréalone

parent compound In chemistry, a parent structure is the structure of an unadorned ion or molecule from which derivatives can be visualized. Parent structures underpin systematic nomenclature and facilitate classification. Fundamental parent structures have one ...

has been studied theoretically, and is unlikely to exist as a stable species. Analogs bearing multiple

substituent In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...

s display

stability Stability may refer to: Mathematics *Stability theory, the study of the stability of solutions to differential equations and dynamical systems ** Asymptotic stability ** Exponential stability ** Linear stability **Lyapunov stability ** Marginal s ...

suitable for synthesis, isolation, and characterization. Substituted montréalones with a balance of

and reactivity have been used as

reaction intermediate In chemistry, a reaction intermediate, or intermediate, is a molecular entity arising within the sequence of a stepwise chemical reaction. It is formed as the reaction product of an elementary step, from the reactants and/or preceding interme ...

s in the synthesis of other heterocycles. Theoretical and experimental analysis of

stable A stable is a building in which working animals are kept, especially horses or oxen. The building is usually divided into stalls, and may include storage for equipment and feed. Styles There are many different types of stables in use tod ...

montréalones reveals overlapping

azomethine ylide Azomethine ylides are nitrogen-based 1,3-dipoles, consisting of an iminium ion next to a carbanion. They are used in 1,3-dipolar cycloaddition reactions to form five-membered heterocycles, including pyrrolidines and pyrrolines. These reactions are ...

and Wittig-type moieties within the unsaturated 5-membered

organophosphorus Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarb ...

ring system. Depending on the phosphorus substituents, ring-chain valence tautomerism allows montréalones to display variable degrees of equilibrium and structural blending with ''N''-acyl amino

phosphonium ylide The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Most o ...

forms. The cyclic 1,3-dipolar form is detectably or exclusively formed with

phosphite The general structure of a phosphite ester showing the lone pairs on the P In organic chemistry, a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR)3. They can be considered as esters of ...

and

phosphonite In organic chemistry, phosphonites are organophosphorus compounds with the formula P(OR)2R. They are found in some pesticides and are used as ligands. Preparation Although they are derivatives of phosphonous acid (RP(OH)2), they are not prepar ...

-based analogs.

Triphenylphosphine Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is versatile compound that is widely used as a reagent in organic synthesis and as a l ...

-based variants lack sufficient tendency for intramolecular cyclization, and exist as acyclic phosphonium ylides. Montrealone resonance and equilibrium structures

Montrealone resonance and equilibrium structures

Synthesis

Montréalones are related to

Wittig reagents In organic chemistry, Wittig reagents are organophosphorus compounds of the formula R3P=CHR', where R is usually phenyl. They are used to convert ketones and aldehydes to alkenes: : Preparation Because they typically hydrolyze and oxidize readily, ...

and can be generated in a similar fashion. Reaction of organophosphorus(III) compounds with ''N''-acyliminium ions affords

phosphonium salt In chemistry, the term phosphonium (more obscurely: phosphinium) describes polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, organyl or halogen group). These cations have tetrahedral structures. The salt ...

intermediates which are

deprotonated Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.ed ...

using non-nucleophilic bases (e.g.

DBU DBU may refer to: Universities * Dallas Baptist University, Dallas, Texas, U.S. * Desh Bhagat University, Mandi Gobindgarh, Punjab, India * Duluth Business University, Duluth, Minnesota, U.S. Other uses * 1,8-Diazabicyclo .4.0ndec-7-ene, an org ...

LiHMDS Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula . 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 ...

). ''N''-Acyliminium ions are generated

in situ is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...

from acid chlorides and

imine In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...

s such that the '

1,3-dipole In organic chemistry, a 1,3-dipolar compound or 1,3-dipole is a dipolar compound with delocalized electrons and a separation of charge over three atoms. They are reactants in 1,3-dipolar cycloadditions. The dipole has at least one resonance st ...

' itself is generated in a

multi-component reaction A multi-component reaction (or MCR), sometimes referred to as a "Multi-component Assembly Process" (or MCAP), is a chemical reaction where three or more compounds react to form a single product. By definition, multicomponent reactions are those re ...

. The most efficient phosphorus(III) precursor for

dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: * An electric dipole moment, electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple ...

synthesis is 2-phenylbenzo 1,3,2]dioxaphosphole catechyl.html" ;"title="hP( catechyl">hP(catechol, catechyl)owing to the balance of nucleophilicity and electrophile, electrophilicity that it affords. Montrealone generation

Reactions

Montréalones participate in 1,3-dipolar cycloaddition reactions with dipolarophiles such as

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

s, and

alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...

s to respectively afford

imidazole Imidazole (ImH) is an organic compound with the formula . It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. It can be classified as a heterocycle, specifically as a diazole. Many natural products, ...

s, 2-

pyrroline Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic organic chemical compounds that differ in the position of the double bond. Pyrrolines are formally derived from the aromate pyrrole by hydrogenation. 1-Pyrroli ...

s, and

pyrrole Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula . It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrol ...

s. The latter

products were obtained by

s involving

-generation of montréalones from

s, acid chlorides, and

s prior to one-pot reactions with the dipolarophile. Moreover, conjugated poly(1,3-dipole) variants of montréalones have been generated and used in the synthesis of polyheterocycles related to

polypyrrole Polypyrrole (PPy) is an organic polymer obtained by oxidative polymerization of pyrrole. It is a solid with the formula H(C4H2NH)nH. It is an intrinsically conducting polymer, used in electronics, optical, biological and medical fields. Histor ...

Cycloaddition reactions of asymmetric

s and dipolarophiles can lead to

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

ic product mixtures, particularly with

münchnone Münchnone (synonyms: 1,3-oxazolium-5-oxide; 1,3-oxazolium-5-olate; anhydro-5-hydroxy-1,3-oxazolium hydroxide; 5-hydroxy-1,3-oxazolium hydroxide, inner salt; oxido-oxazolium) is a mesoionic heterocyclic compound, heterocyclic aromatic chemical com ...

s and

s in the synthesis of

s. In contrast to related Diels-Alder reactions, rationalization of regioisomeric bias using conventional frontier molecular orbital (FMO) theory fails. The complementary use of montéalones and münchnones allows product mixtures to be avoided and highlights the need to consider transition-state geometrical changes (distortion) in the rationalization process. Montrealone vs munchnone cycloaddition

References

{{DEFAULTSORT:Montrealone Oxygen heterocycles Phosphorus heterocycles Nitrogen heterocycles Five-membered rings Organophosphine oxides Heterocyclic compounds with 1 ring

Structure

Synthesis

Reactions

See also

References