Aromatic allene compounds

In the 1980 s three monographs were published that cover parts of the present book, namely Quinone Diazides, by Ershov, Nikiforov, and de Jonge (1981), Aromatic Diazo Compounds, by Saunders and Allen (1985), and Williams Nitrosa-tion (1988). The book of Saunders and Allen which is actually the third edition of Saunders original book (1936, 1949), focuses on synthesis and preparative methods. The other two books emphasize rather the mechanistic and physical organic aspects of their subjects. 

K H Saunders and R L M Allen, Aromatic diazo compounds, 3rd Edn (London Edward Arnold, 1985). 

H. Zollinger, Azo and Diazo Chemistry, Interscience, New York, 1961 S. Patai, ed. The Chemistry of Diazonium and Diazo Groups, John Wiley Sons, New York, 1978, Chapters 8,11, and 14 H. Saunders and R. L. M. Allen, Aromatic Diazo Compounds, 3rd ed., Edward Arnold, London, 1985. 

K. H. Saunders and R. L. M. Allen, Aromatic Diazo Compounds, Edward Arnold, London, 1985. 

K.H. Saunders u. R.L.M. Allen, Aromatic diazo Compounds, 3. Aufl., S. 71 ff., Edward Arnold, London 1985. 

The present method is the result of a study by Cason, Harman, Goodwin, and Allen.6 7 The sequence of electrolytic reduction followed by oxidation has been used for the preparation of 5-bromotoluquinone,8 5-chlorotoluquinone,9 and 3-chlorotolu-quinone.10 The preparation of an intermediate />-aminophenol from the corresponding aromatic nitro compound by electrolytic reduction is a useful general method.11-18 Chloro-/>-quinone has been prepared by acid dichromate oxidation of chlorohydro-quinone 19-22 or 2-chloro-4-aminophenol.23 24 It has been shown that pure chloro-/>-quinone is obtained only with some difficulty when chlorohydroquinone is used.7... 

Pinacol yields are normally better with aromatic carbonyl compounds. Some examples are given in Table 14. A more extensive coverage - especially of the older literature - has been given by Allen 6 Popp and Schultz 9 and Fichter 4). 

Reaction of lithiated allene with methoxymethyl isothiocyanate afforded 107, after trapping with methyl iodide. The newly formed 107 isomerizes under mild conditions to triene 108. This compound is ideally setup to experience an electrocyclization to dihydropyridine 109. Heating in the presence of acid facilitates aromatization of 109 to pyridines 110. 

Further exploitation of the molecular shape feature has led more recently to the design of another series of clathrate hosts by substituting on the allene rigid backbone bulky groups 22>, Representative compounds of this new host family are 20 and 21. The allene 20 (R = t-butyl) shows an interesting clathration behaviour upon crystallization from various environments, including alicyclic and aromatic compounds, heterocycles, cyclic ketones and eyclohexaneamine 26>. 

The allene host 20 exhibits high inclusion selectivity in competition experiments using mixtures of solvents 26). In fact, preliminary results indicate that it can be used for the separation of constitutional isomers, of homologues, and of aliphatic from alicyclic or aromatic compounds (Table 3). Other derivatives of the allene, e.g. 21, are also functional as host molecules, and are currently being subjected to further investigations 22). 

The cydoaddition of different 1,3-dipoles such as azides [331, 341] and diazoalkanes [342-344] to acceptor-substituted allenes was thoroughly investigated early and has been summarized in a comprehensive review by Broggini and Zecchi [345], The primary products of the 1,3-dipolar cycloadditions often undergo subsequent fast rearrangements, for example tautomerism to yield aromatic compounds. For instance, the five-membered heterocycles 359, generated regioselectively from allenes 357 and diazoalkanes 358, isomerize to the pyrazoles 360 (Scheme 7.50) [331]. 

Abstract The basic principles of the oxidative carbonylation reaction together with its synthetic applications are reviewed. In the first section, an overview of oxidative carbonylation is presented, and the general mechanisms followed by different substrates (alkenes, dienes, allenes, alkynes, ketones, ketenes, aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, phenols, amines) leading to a variety of carbonyl compounds are discussed. The second section is focused on processes catalyzed by Pdl2-based systems, and on their ability to promote different kind of oxidative carbonylations under mild conditions to afford important carbonyl derivatives with high selectivity and efficiency. In particular, the recent developments towards the one-step synthesis of new heterocyclic derivatives are described. 

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