Isoindoles, reviews

Isoindole (1) and its analogs, isobenzofuran (2) and isothianaphthene (3), have attracted considerable theoretical and synthetic interest. -Of the jjarent heterocycles, only isothianaphthene (3) has proved sufficiently stable for isolation, - although both (1) and (2) have been detected as transient species, and it seems likely that a more complete characterization will be forthcoming with improved experimental techniques. This review is concerned with the chemistry of... 

In carbocyclic chemistry, rather firm dividing lines usually exist between aromatic, non-aromatic, and anti-aromatic compounds, while in heterocyclic chemistry enormous variations in the extent of aromatic character are displayed.52 Furthermore, there is an enormous number of potential heterocycles as compared to carbocycles, as will be detailed in section 3 of this review. The degree of aromaticity has classically been judged qualitatively in connection with the diene character of heterocycles manifested in Diels— Alder reactions or polymerizations. In this regard for instance, furan (42) is less aromatic than benzene (43), as is isoindole (44) compared to indole (45) (Scheme 18). Therefore, a quantitative aromaticity scale would be useful. 

The chemistry of the o-quinonoidal heterocycles benzo[c] indole (isoindole, 1) and benzo[< ]thiophene (2) has been previously reviewed in this... 

Dimethyl acetylenedicarboxylate and 1 -methylpyrrole combine yielding mainly the dihydroindole 6. This is readily explained by assuming that the adduct 5 is first formed and that it then combines with a second molecule of the ester as indicated.71 This reaction has already been reviewed,1 and, although attempts to isolate compound 5 have failed, a corresponding compound in the isoindole series192 has been obtained and gives the appropriate analog of 6 with more of the acetylenic ester. 

A fundamental chemical tactic in the synthetic manipulation of heterocycies by organic chemists is the reduction of the heterocyclic ring. This chapter will review advances in the partial and complete reduction of pyrroles, furans, thiophenes and their benzo analogs, indoles, benzo[Z>]furans and benzo[Z>]thio-phenes. As appropriate, coverage will include the reduction of those benzo analogs of lesser interest isoindole, carbazole, benzo[c]furan (isobenzofuran), dibenzofuran and dibenzothiophene. 

The isomeric isoindoles are very susceptible to reduction. But because no new methods to accomplish this reduction have been reported in the years since an excellent review was published over 20 years ago, nothing further on this topic will be presented here. 

Claessens et al. reviewed the recent progress in studies of NLO properties of boron-subphthalocyanines (SubPcs). These phthalocyanine derivatives consist of three isoindole units N-fused around a central boron atom, which bear an axial ligand. These authors noted that the optical response of these nearly ocmpolar derivatives is associated to the charge transfer inside the macrocycle tt surface. Ihey... 

There are general reviews on heterocyclic syntheses by cycloaddition reactions of isocyanates and on the use of heterocyclic cations in preparative organic chemistry. More specific topics are 5-hydroxymethylfuran-2-carb-aldehyde, isobenzofurans and related ort/io-quinonoid systems, the conversion of 2//-cyclohepta[Zj] furan-2-one (1) into derivatives of azulene, the synthesis of indoles from o-alkylphenyl isocyanides, and abnormal Fischer indolization reactions of o-methoxyphenylhydrazones. Two reviews on isoindoles have appeared and a lecture on highly conducting charge-transfer complexes that are based on heterocyclic selenium and tellurium donors has been reprinted.Recent advances in the chemistry of imidazole and in the use of nitro-imidazoles as radiosensitizers have been summarized. There have been reviews on benzimidazole A -oxides and on dihydrobenzimidazoles, benzimidazolones, benzimidazolethiones, and related compounds. Other topics are synthetic applications of 1,3-dithiolium and 1,3-oxathiolium salts and of isoxazoles, the chemistry of benzisoxazoles, 2-amino-oxazoles, 5-oxazolones (2), furoxans, benzofuroxans, and related systems, the synthesis of five-membered meso-ionic compounds, and tetrazoles. ... 

The isoindoles were reviewed in this series by White and Mann in 1969,5 Since that time there has been a considerable expansion in isoindole chemistry, including, in 1972, the isolation and characterization of the parent system.6 The present review concentrates on developments since 1969, but a certain amount of chemistry from earlier years is included where appropriate. Throughout, the use of the name isoindole in a general context does not imply the absence of the 1 H-isoindole (isoindolenine) tautomer (2) if... 

Several 7t-annelated isoindole systems, of which 23 is an example, have been described in recent years38-43 but are outside the scope of this review. 

Various routes to 1,1,3-trisubstituted 1//-isoindoles have been reviewed.5 Thus, the triphenyl derivative 53 is available from the reaction of benzo-phenone imine with diphenyldichloromethane or by the Friedel-Crafts reactions between benzene and l,l,3-trichloro-lf/-isoindole. Recently, another route, which involves heating the cyclotriphosphatriazene 54 with benzophenone, has been described.86 The nitrone derivative 55 of the isoindolenine 53 may be obtained by treating the isoindolenine with m-chloroperbenzoic acid. This nitrone has also been obtained by the isomerization of the oxaziran 56 in the presence of a Lewis acid (Scheme 11).87... 

Volume 29 consists of six contributions. Three of these deal with specific groups of compounds and update previous contributions in this publication on the same type of compounds. Thus, R. K. Smalley, who writes on The Chemistry of Indoxazenes and Anthranils 1966-1979, updates the article by Wunsch and Boulton published in 1967 in Volume 8. Raymond Bonnett and Stephanie A. North, writing on The Chemistry of the Isoindoles, update the contribution by White and Mann, published in Volume 10, in 1969, and Richard M. Scrowston, with his review entitled, Recent Advances in the Chemistry of Benzo[fe]-thiophenes, updates that by himself and Iddon in Volume II, published in 1970. The chemistry of Furoxans and Benzofuroxans is covered by A. Gasco and A. J. Boulton. This and the subject of Mononuclear Heterocyclic Rearrangements reviewed by Michele Ruccia, Nicolb Vivona, and Domenico Spinelli, are both topics close to the hearts of the Editors of this volume. Finally, Yasumitsu Tamura and Masazumi Ikeda have summarized Advances in the Chemistry of Heteroaromatic N-Imines and N-Aminoazonium Salts. Although this subject was reviewed as recently as 1974, in Volume 17 of Advances, its growth since then has been so dramatic that this further review is very timely. 

Uses of bases of this type, such as DBU and DBN have been reviewed [15] and more recently they have been used as stoichiometric bases in the synthesis of 2H-isoindoles [ 16],biaryl thioethers [17],phthalocyanines [18] and the related macrocyclic compounds [18], 2,4-dioxo-l,2,3,4-tetrahydroquinazolines [19], dihydro alanine-containing peptides [20] and [[pyrazolylmethyl)amino]-propyl azepinones and -pyrrolidinones [21]. Chiral DBU/DBN-related molecules have also been synthesized which were fovmd to be useful as catalysts in an asymmetric Michael reaction [22]. 

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