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In organic chemistry, spiro compounds are compounds that have at least two molecular rings with only one common atom. The simplest spiro compounds are bicyclic (having just two rings), or have a bicyclic portion as part of the larger ring system, in either case with the two rings connected through the defining single common atom. [3] : SP-0 [4] : 653, 839 The one common atom connecting the participating rings distinguishes spiro compounds from other bicyclics: from isolated ring compounds like biphenyl that have no connecting atoms, from fused ring compounds like decalin having two rings linked by two adjacent atoms, and from bridged ring compounds like norbornane with two rings linked by two non-adjacent atoms. [5] [4] : 653ff : 839ff
Spiro compounds may be fully carbocyclic (all carbon) or heterocyclic (having one or more non-carbon atom). One common type of spiro compound encountered in educational settings is a heterocyclic one— the acetal formed by reaction of a diol with a cyclic ketone. The common atom that connects the two (or sometimes three) rings is called the spiro atom; [3] : SP-0 in carbocyclic spiro compounds like spiro[5.5]undecane (see image at right), the spiro-atom is a quaternary carbon, and as the -ane ending implies, these are the types of molecules to which the name spirane was first applied (though it is now used general of all spiro compounds). [6] : 1138ff Likewise, a tetravalent neutral silicon or positively charged quaternary nitrogen atom (ammonium cation) can be the spiro center in these compounds, and many of these have been prepared and described. [6] : 1139f [ citation needed ] The 2-3 rings being joined are most often different in nature, though they, on occasion, be identical [e.g., spiro[5.5]undecane, just shown, and spiropentadiene, at right]. Although sketches of organic structures makes spiro compounds appear planar, they are not; for instance, a spiro compound with a pair of three-membered cyclopropene rings connected in spiro fashion (image below) has been given the popular misnomer of being a bow tie structure, when it is not flat or planar like a bow tie. This can be stated another way, saying that the best-fit planes to each ring are often perpendicular or are otherwise non-coplanar to one another. [4] : 319f.846f
Spiro compounds are present throughout the natural world, some cases of which have been exploited to provide tool compounds for biomedical study and to serve as scaffolds for the design of therapeutic agents with novel shapes.[ citation needed ] As well, the spiro motif is present in various practical compound types (such as dyes), as well as in a wide variety of oligo- and polymeric materials designs, for the unique shapes and properties the spiro center imparts, e.g., in the design of electronically active materials in particular.[ citation needed ] In both cases, the presence of the spiro center, often with four distinct groups attached, and with its unique aspects of chirality, adds unique challenges to the chemical synthesis of each compound type.[ citation needed ]
Bicyclic ring structures in organic chemistry that have two fully carbocyclic (all carbon) rings connected through just one atom are present both in natural products, [7] as well as in esoteric targets of chemical synthesis.[ citation needed ] The two carbocycles can be different in nature, or identical. In common targets derived from natural products, they are essentially always different. [7] In esoteric targets, such as highly strained hydrocarbons like spiropentadiene, shown here, the rings can be identical. The atom connecting the two rings is called the spiro-atom; in carbocyclic spiro compounds, the spiro-atom is a quaternary carbon. The 11-carbon bicyclic structure shown above, spiro[5.5]undecane, is also a fully carbocyclic spiro compound. While the presentation of this structure makes it appear fully planar, it is not. The best-fit planes to each six-atom ring above is near to perpendicular, and the best-fit planes to rings of spiro compounds are likewise generally non-coplanar. For instance, the structure of faux bow tie spiropentadiene, shown above, makes clear that the planes that are defined by the atoms of each ring—i.e., the best-fit plane of each cyclopropene—are orthogonal (perpendicular) to one another. [8]
Spiro compounds are considered heterocyclic if the spiro atom or any atom in either ring are not carbon atoms. Cases include the presence of a spiro heteroatom such silicon and nitrogen (but also other Group IVA [14] and other atom types) connecting the rings that have been observed or are under theoretical study; [6] : 1139f [ citation needed ] moreover, there are also many cases where one or more heteroatoms appear in one or more of the rings that are joined at a carbon spiro atom (e.g., where 1 oxygen spironolactones and 2 oxygen/2 sulfur ketals/thioketals are very common).[ citation needed ] [9] [ verification needed ]
A common case is the presence of two atoms that are not carbon in one of the rings, with those two rings both attached to the spiro atom; indeed, often the earliest exposure of a chemist in training to a spiro compound is to a heterocyclic form, the ketal (acetal) formed in the protection of ketones by diols and dithiols. An example of this is shown above, in the synthesis of the acetal 1,4-dioxaspiro[4.5]decane from cyclohexanone and ethanediol. In this case, because the four atoms attached to the spiro atom are not all carbons, the spiro atom is not a quaternary carbon. A further example of an acetal formed from a cyclic ketone, except with a dithiol, is the spiro compound spirapril, which has a five-membered ring formed from 1,2-ethanedithiol. Again, while the rings could be identical, in the heterocyclic case they are, again, almost always non-identical. Once again, the best-fit planes to each ring are generally non-coplanar to one another (i.e., the rings are not coplanar, despite appearing so in images).
A polyspiro compound is connected by two or more spiroatoms making up three or more rings.[ citation needed ]
Nomenclature for spiro compounds was first discussed by Adolf von Baeyer in 1900. [10] The prefix spiro denotes two rings with a spiro junction. The main method of systematic nomenclature is to follow with square brackets containing the number of atoms in the smaller ring then the number of atoms in the larger ring, separated by a period, in each case excluding the spiroatom (the atom by which the two rings are bonded) itself. Position-numbering starts with an atom of the smaller ring adjacent to the spiroatom around the atoms of that ring, then the spiroatom itself, then around the atoms of the larger ring. [11] For example, compound A in the image is called 1-bromo-3-chlorospiro[4.5]decan-7-ol, and compound B is called 1-bromo-3-chlorospiro[3.6]decan-7-ol.
Spiranes can be chiral, in three distinct ways. [6] : 1138ff First, while nevertheless appearing to be twisted, they yet may have a chiral center making them analogous to any simple chiral compound, and second, while again appearing twisted, the specific location of substituents, as with alkylidenecycloalkanes, may make a spiro compound display central chirality (rather than axial chirality resulting from the twist); third, the substituents of the rings of the spiro compound may be such that the only reason they are chiral arises solely from the twist of their rings, e.g., in the simplest bicyclic case, where two structurally identical rings are attached via their spiro atom, resulting in a twisted presentation of the two rings. [6] : 1138ff, 1119ff [4] : 319f.846f Hence, in the third case, the lack of planarity described above gives rise to what is termed axial chirality in otherwise identical isomeric pair of spiro compounds, because they differ only in the right- versus left-handed "twist" of structurally identical rings (as seen in allenes, sterically hindered biaryls, and alkylidenecycloalkanes as well). [6] : 1119f Assignment of absolute configuration of spiro compounds has been challenging, but a number of each type have been unequivocally assigned. [6] : 1139ff
Some spiro compounds exhibit axial chirality. Spiroatoms can be the origin of chirality even when they lack the required four different substituents normally observed in chirality. When two rings are identical the priority is determined by a slight modification of the CIP system assigning a higher priority to one ring extension and a lower priority to an extension in the other ring. When rings are dissimilar the regular rules apply.[ clarification needed ]
Spiro compounds present unique preparative challenges, whether each ring contributing to its structure is unique or identical, or whether they are carbocyclic or heterocyclic—owing to the practical implications of tetra-functionalizing the central spiro atom (often with four different groups), and of the unique aspects of chirality that apply to these compounds. [9] [ verification needed ]
Some spiro compounds can be synthesized using the Pinacol-pinacolone rearrangement; [4] : 985 for example, spiro[4.5]decane (final compound in following two line scheme) can be synthesized from symmetric 1,2-diols of the sort shown below [e.g., this route's starting material, (1,1′-bicyclopentyl)-1,1′-diol [12] ]. Initially, one of the carbinol moieties is protonated, allowing water to leave, and yielding the corresponding carbocation (second structure, first row); this intermediate then undergoes a bond migration, resulting in ring expansion of the adjacent ring, with deprotionation unmasking the ketone functional group to complete the first line of the mechanism. This first product, a spirobicyclic ketone, is a spiro compound in its own right, and yields the further spiro carbinol and the alicyclic spiro hydrocarbon after two further reduction reactions. First, reduction of the carbonyl that ends the mechanism's first line provides the spiro carbinol starting material of the second line, which is needed for reduction to the alkane (shown). This latter reduction is accomplished using lithium aluminium hydride (LiAlH4), via the alcohol tosylate (formed using tosyl chloride). Hence this three reaction sequence provides three spiro compounds (ketone, alcohol, and alkane), of possible research or practical use. [4] : 985 [ verification needed ]
Spiro forms of lactones and oxazines are frequently used as leuco dyes, frequently displaying chromism—reversible structural change between forms giving rise to colorless and colored appearances, especially in solution.[ citation needed ]
Spiroaromaticity in organic chemistry refers to a special case of aromaticity in which conjugation is interrupted by a single spiroatom. Although this spiro center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties associated with aromatic compounds are still observed for such compounds.
A spiro compound, or spirane, from the Latin spīra, meaning a twist or coil, [13] [6] : 1138 [14] is a chemical compound, typically an organic compound, that presents a twisted structure of two or more rings (a ring system), in which 2 or 3 rings are linked together by one common atom, [3] : SP-0 examples of which are shown at right.
In organic chemistry, the Cahn–Ingold–Prelog (CIP) sequence rules are a standard process to completely and unequivocally name a stereoisomer of a molecule. The purpose of the CIP system is to assign an R or S descriptor to each stereocenter and an E or Z descriptor to each double bond so that the configuration of the entire molecule can be specified uniquely by including the descriptors in its systematic name. A molecule may contain any number of stereocenters and any number of double bonds, and each usually gives rise to two possible isomers. A molecule with an integer n describing the number of stereocenters will usually have 2n stereoisomers, and 2n−1 diastereomers each having an associated pair of enantiomers. The CIP sequence rules contribute to the precise naming of every stereoisomer of every organic molecule with all atoms of ligancy of fewer than 4.
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, properties, and applications of organic heterocycles.
Monosaccharides, also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built. Simply this is the structural unit of carbohydrates.
In organic chemistry, an aldehyde is an organic compound containing a functional group with the structure R−CH=O. The functional group itself can be referred to as an aldehyde but can also be classified as a formyl group. Aldehydes are a common motif in many chemicals important in technology and biology.
In organic chemistry, an acetal is a functional group with the connectivity R2C(OR')2. Here, the R groups can be organic fragments or hydrogen, while the R' groups must be organic fragments not hydrogen. The two R' groups can be equivalent to each other or not. Acetals are formed from and convertible to aldehydes or ketones and have the same oxidation state at the central carbon, but have substantially different chemical stability and reactivity as compared to the analogous carbonyl compounds. The central carbon atom has four bonds to it, and is therefore saturated and has tetrahedral geometry.
In organic chemistry, the cycloalkanes are the monocyclic saturated hydrocarbons. In other words, a cycloalkane consists only of hydrogen and carbon atoms arranged in a structure containing a single ring, and all of the carbon-carbon bonds are single. The larger cycloalkanes, with more than 20 carbon atoms are typically called cycloparaffins. All cycloalkanes are isomers of alkenes.
In chemical nomenclature, the IUPAC nomenclature of organic chemistry is a method of naming organic chemical compounds as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in the Nomenclature of Organic Chemistry. Ideally, every possible organic compound should have a name from which an unambiguous structural formula can be created. There is also an IUPAC nomenclature of inorganic chemistry.
A diol is a chemical compound containing two hydroxyl groups. An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified.
A bicyclic molecule is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic, or heterocyclic, like DABCO. Moreover, the two rings can both be aliphatic, or can be aromatic, or a combination of aliphatic and aromatic.
Cyclohexane conformations are any of several three-dimensional shapes adopted by molecules of cyclohexane. Because many compounds feature structurally similar six-membered rings, the structure and dynamics of cyclohexane are important prototypes of a wide range of compounds.
Dioxolane is a heterocyclic acetal with the chemical formula (CH2)2O2CH2. It is related to tetrahydrofuran (THF) by replacement of the methylene group (CH2) at 2nd position of THF with an oxygen atom. The corresponding saturated 6-membered C4O2 rings are called dioxanes. The isomeric 1,2-dioxolane (wherein the two oxygen centers are adjacent) is a peroxide. 1,3-dioxolane is used as a solvent and as a comonomer in polyacetals.
The Danishefsky Taxol total synthesis in organic chemistry is an important third Taxol synthesis published by the group of Samuel Danishefsky in 1996 two years after the first two efforts described in the Holton Taxol total synthesis and the Nicolaou Taxol total synthesis. Combined they provide a good insight in the application of organic chemistry in total synthesis.
A cyclic compound is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon, none of the atoms are carbon, or where both carbon and non-carbon atoms are present. Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, carbocyclic and heterocyclic compounds may be aromatic or non-aromatic; in the latter case, they may vary from being fully saturated to having varying numbers of multiple bonds between the ring atoms. Because of the tremendous diversity allowed, in combination, by the valences of common atoms and their ability to form rings, the number of possible cyclic structures, even of small size numbers in the many billions.
Barrelene is a bicyclic organic compound with chemical formula C8H8 and systematic name bicyclo[2.2.2]octa-2,5,7-triene. First synthesized and described by Howard Zimmerman in 1960, the name derives from the resemblance to a barrel, with the staves being three ethylene units attached to two methine groups. It is the formal Diels–Alder adduct of benzene and acetylene. Due to its unusual molecular geometry, the compound is of considerable interest to theoretical chemists.
A fenestrane in organic chemistry is a type of chemical compound with a central quaternary carbon atom which serves as a common vertex for four fused carbocycles. They can be regarded as spiro compounds twice over. Because of their inherent strain and instability, fenestranes are of theoretical interest to chemists. The name—proposed in 1972 by Vlasios Georgian and Martin Saltzman—is derived from the Latin word for window, fenestra. Georgian had intended that "fenestrane" solely referred to [4.4.4.4]fenestrane, whose skeletal structure looks like windows, and Kenneth B. Wiberg called that specific structure "windowpane". The term fenestrane has since become generalized to refer to the whole class of molecules that have various other ring-sizes. Georgian recommended rosettane for the class, based on the structural appearance as a rosette of flowers.
The Mukaiyama taxol total synthesis published by the group of Teruaki Mukaiyama of the Tokyo University of Science between 1997 and 1999 was the 6th successful taxol total synthesis. The total synthesis of Taxol is considered a hallmark in organic synthesis.
Trimethylenemethane cycloaddition is the formal [3+2] annulation of trimethylenemethane (TMM) derivatives to two-atom pi systems. Although TMM itself is too reactive and unstable to be stored, reagents which can generate TMM or TMM synthons in situ can be used to effect cycloaddition reactions with appropriate electron acceptors. Generally, electron-deficient pi bonds undergo cyclization with TMMs more easily than electron-rich pi bonds.
In chemistry, a ring is an ambiguous term referring either to a simple cycle of atoms and bonds in a molecule or to a connected set of atoms and bonds in which every atom and bond is a member of a cycle. A ring system that is a simple cycle is called a monocycle or simple ring, and one that is not a simple cycle is called a polycycle or polycyclic ring system. A simple ring contains the same number of sigma bonds as atoms, and a polycyclic ring system contains more sigma bonds than atoms.
In chemical nomenclature, a descriptor is a notational prefix placed before the systematic substance name, which describes the configuration or the stereochemistry of the molecule. Some listed descriptors are only of historical interest and should not be used in publications anymore as they do not correspond with the modern recommendations of the IUPAC. Stereodescriptors are often used in combination with locants to clearly identify a chemical structure unambiguously.
3,9-Divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane (DVTOSU) is a bicyclic organic molecule having a central quaternary carbon atom with which two alicyclic rings are linked, each comprising five atoms. DVTOSU is a diallyl acetal and the precursor for the isomeric ketene acetal monomer 3,9-diethylidene-2,4,8,10-tetraoxaspiro[5.5]undecane (DETOSU) which is a building block for polyorthoesters.
Die Übersetzung basiert auf der "Extension and Revision of the Nomenclature for Spiro Compounds" der Commission on Nomenclature of Organic Chemistry (III.1) der Organic Chemistry Division der International Union of Pure and Applied Chemistry, veröffentlicht in Pure Appl. Chem. 1999, 71, 531–558.
Quoting: 'spīra ae, f, σπεῖρα, a coil, fold, twist, spiral: in spirain se conligit anguis, V., O.: longo iactetur spira galero, i. e. tie, Iu.'The Greek transcription, σπεῖρα, reflects the use of this cognate as one ancient Greek term to refer to a coil or related fold, see Woodhouse, S.C. (1910). "Fold, subs. [dictionary entry]". English-Greek Dictionary: A Vocabulary of the Attic Language. Ludgate Hill [London, ENG]: George Routledge & Sons. Retrieved 3 February 2016.
Quoting: 'Fold, subs. … Coil : V. σπεῖρα… see coil.'