Banert / Nielsen / Ameduri Science of Synthesis Knowledge Updates 2014 Vol. 3

1. Auflage 2014
ISBN: 978-3-13-176301-3
Verlag: Thieme
Format: PDF
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 536 Seiten, PDF, Format (B × H): 170 mm x 255 mm

Reihe: Science of Synthesis

The Science of Synthesis Editorial Board,together with the volume editors and
authors, is constantly reviewing the whole field of synthetic organic chemistry
as presented in Science of Synthesis and evaluating significant developments in
synthetic methodology. Four annual volumes updating content across all
categories ensure that you always have access to state-of-the-art synthetic
methodology.

Content of this volume:

Five#Five-Fused Hetarenes with One Heteroatom in Each Ring; One Oxygen and
One Nitrogen or Phosphorus Atom; One Sulfur, Selenium, or Tellurium Atom and One
Nitrogen or Phosphorus Atom; Carbon Dioxide, Carbonyl Sulfide, Carbon Disulfide,
Isocyanates, Isothiocyanates, Carbodiimides, and Their Selenium, Tellurium, and
Phosphorus Analogues; 1,1-Dihaloalk-1-enes; Bis(heteroatom-functionalized)
Acetylenes; 1-Haloalk-1-ynes and Alk-1-yn-1-ols; Diazo Compounds;
Alkaneselenolates of Group 3#12 Metals; Cyclic Alkaneselenolates of Group 3#12
Metals; Alkanetellurolates of Group 3#12 Metals; Cyclic Alkanetellurolates of
Group 3#12 Metals.

Zielgruppe

Wissenschaftler

Autoren/Hrsg.

Ameduri, Bruno

Banert, Klaus

Braverman, Samuel

Nielsen, Mogens Brøndsted

Drabowicz, Jozef

Joule, John A.

Schaumann, Ernst

Weinreb, Steven M.

Fachgebiete

• Naturwissenschaften Chemie Organische Chemie

Leseproben

10.21 Product Class 21: Five–Five-Fused Hetarenes with One Heteroatom in Each Ring

S. P. Stanforth

General Introduction

Five–five-fused hetarenes with one heteroatom in each ring are conveniently categorized into four classes of hetaryl[n,m-]hetarenes 2–5, which recognizes their isoelectronic relationship to the pentalene dianion 1 (? Scheme 1). This method of classification is adopted in three previous reviews covering this class of heterocyclic compounds.[1–3] In these reviews, the description of heterocycles as n,m-diheteropentalenes is used and this nomenclature is commonly encountered in the literature. In this chapter, the five–five-fused hetarenes will be described as hetaryl[n,m-]hetarenes because this is consistent with the nomenclature used throughout . The relationship between these two systems of nomenclature is shown in ? Scheme 1. Note that in the case of the heterocycles represented by the general structure 3, these structures are either [2,3-]- or [3,4-]-fused systems depending upon the nature of the heteroatoms X and Z (see ? Scheme 2). The hetaryl[n,m-]hetarenes 2–4 can all be represented as covalent structures whereas the hetaryl[3,4-]hetarene system can be depicted by either the 1,3-dipolar structure 5 or an alternative “non-classical”covalent representation when at least one of the component heteroatoms, for currently known systems, comprises sulfur, selenium, or tellurium. Both representations are found in the literature. The hetaryl[3,4-]hetarene system 5 is associated with a highest occupied molecular orbital that is similar in topology and energy to a nonbonding molecular orbital.[4] This feature distinguishes the hetaryl[3,4-]hetarenes 5 from the other heterocycles 2–4. Substitution of the carbanion centers in structures 1A–1C with heteroatoms (and their associated lone pair of electrons) leads to the covalent hetaryl[n,m-]hetarenes structures 2–4, respectively. In contrast, when substituting an alkenyl carbon atom in structure 1B with a heteroatom, the structure 5 is produced.

Scheme 1 Hetaryl[n,m-]hetarenes and the Pentalene Dianion

There are 21 possible hetaryl[n,m-]hetarene structures associated with each of the general formulae 2, 4, and 5 and 36 possible structures associated with the general formula 3 when the heteroatoms X and Z are chosen from oxygen, sulfur, selenium, tellurium, nitrogen, and phosphorus. This gives a total of 99 potential hetaryl[n,m-]hetarene systems. Many of these systems are as yet unknown. Hetaryl[n,m-]hetarenes that comprise either a tellurophene or phosphole ring fused to any other five-membered ring are relatively rare. In contrast, there is extensive literature relating to heterocycles comprising two fused thiophene rings, partly as a consequence of interest in these systems as polythiophene analogues in materials chemistry. Hetaryl[n,m-]hetarenes that possess a pyrrole ring fused to another ring have attracted interest as indole analogues.

The IUPAC nomenclature of the hetaryl[n,m-]hetarenes is derived from a fusion of the names of the two constituent five-membered heterocyclic rings, i.e. furan, thiophene, selenophene, tellurophene, pyrrole, and phosphole. This is illustrated in ? Scheme 2 for the thiophene–pyrrole ring fusion modes. Note that the hetaryl[2,3-]hetarenes/hetaryl[3,4-]hetarenes are unsymmetrical and two possible isomers can exist: for example, 5-thieno[2,3-]pyrrole and 1-thieno[3,4-]pyrrole. In the old literature, the thienothiophenes 2, 3, and 4 (X = Z = S) are collectively named “thiophthens”but this terminology is not found in the modern literature. Similarly, the name “selenophthen”was used in the past for selenophenoselenophenes. For hetaryl[n,m-]hetarenes possessing a selenium-containing ring, both the constructions selenopheno[n,m-]hetarene and selenolo[n,m-]hetarene (preferred) are encountered in the literature. There are several related methods for naming the hetaryl[3,4-]hetarene ring systems that are found in the literature, all of which include the basic stem for naming the two fused rings. This is illustrated for the hetaryl[3,4-]hetarene system 5 (X = Z = S), derivatives of which have been named as thieno[3,4-]thiophenes, SIV-thieno[3,4-]thiophenes (to take into account the nonstandard valence state of the sulfur atom), or more recently as 2?4d2-thieno[3,4-]thiophenes. The hetaryl[3,4-]hetarenes 5 are members of a class of heterocyclic molecules described as “heteropentalene mesomeric betaines”or “non-classical heteropentalenes”, a categorization which reflects their 1,3-dipolar nature.[4]

Scheme 2 IUPAC Nomenclature of Hetaryl[n,m-]hetarenes as Represented by the Thiophene–Pyrrole Fusion Modes

The five–five-fused hetarenes with one heteroatom in each ring have not been previously reviewed in . A preliminary review in 1984[1] and two subsequent updates from 1996[2] and 2006[3] detailing aspects of the synthesis, chemistry, and physical properties of hetaryl[n,m-]hetarenes have appeared. Two substantial reviews from 1976 and 2006 covering the preparation and chemistry of the various thienothiophene ring systems have also been published.[5,6] Azapentalenes (i.e., heterocyclic systems in which one or more of the carbon atoms in the pentalene dianion 1 are replaced with nitrogen) have also been reviewed.[7] Heteropentalene mesomeric betaines, of which the hetaryl[3,4-]hetarene system 5 is a representative structure, have been reviewed.[4]

As a consequence of their isoelectronic relationship with the pentalene dianion 1, the hetaryl[n,m-]hetarenes 2–5 exhibit aromatic character because they are associated with 10 p-electrons. The chemistry of these bicyclic systems reflects this aromatic character and the reactivity profile of their constituent five-membered rings. Thus, electrophilic substitution and C— H metalation reactions are well-known and these processes are described in appropriate sections of this review. These reactions allow the synthesis of hetaryl[n,m-]hetarenes by substituent modification. One class of reaction that differentiates between the various hetaryl[n,m-]hetarene systems are cycloaddition reactions. Numerous cycloaddition reactions of the hetaryl[2,3-]hetarene, hetaryl[3,4-]hetarene, and hetaryl[3,4-]hetarene systems have been reported and representative examples can be found in the review articles.[1–4] In contrast, the cycloaddition chemistry of other hetaryl[n,m-]hetarene systems is comparatively rare; some examples of the reactions of furo[3,2-]pyrroles with electron-deficient alkynes are known and these have been reviewed.[2] It is noteworthy that although several examples of the parent hetaryl[n,m-]-hetarenes 2–4 have been isolated and characterized, this is not the case for the parent hetaryl[3,4-]hetarenes 5, which are too reactive to enable isolation.

Experimental structural methods that can be used in the characterization of hetaryl[n,m-]hetarenes have been reviewed in depth.[1–6] The methods discussed include NMR spectroscopy (1H, 13C, 15N, 77Se), UV spectroscopy, IR spectroscopy, mass spectrometry, photoelectron spectrometry, electron paramagnetic resonance, dipole moments, polarography, and X-ray diffraction studies. The melting points of several of the parent hetaryl[n,m-]hetarene systems have also been tabulated.[2] Also included in the review articles are theoretical studies of the hetaryl[n,m-]hetarenes, which generally support the categorization of these molecules as electron-rich aromatic heterocycles. The role of sulfur 3d orbital participation in the hetaryl[3,4-]hetarenes 5 (X or Z = S) has been debated.
Brief mention should also be made of hetaryl[n,m-]hetarene derivatives that are isoelectronic with pentalene 6. Such heterocycles are therefore associated with 8 p-electrons and are formally antiaromatic. Examples of this class of heterocycle (? Scheme 3) include the stable pyrrolo[3,4-]pyrrole (2,5-diazapentalene) derivative 7[8] and the pyrrolo[3,2-]pyrrole (1,4-diazapentalene) derivative 8, which is reported to be unstable in air at room temperature.[9]

Scheme 3 Pentalene and Antiaromatic Pyrrolopyrrole Derivatives[8,9]

In order to maintain consistency in the depiction of the...