Unsaturated nitrogen heterocyclic compounds

The Chemistry of Unsaturated Nitrogen-Heterocyclic Compounds Containing Carbonyl Groups... 

The synthesis of oxygen- and nitrogen-containing heterocyclic compounds by anionic cyclization of unsaturated organolithium compounds has been reviewed recently. " Broka and Shen reported the first intramolecular reaction of an unstabilized a-amino-organolithium compound using reductive lithiation of an A,5-acetal derived from a homoaUylic secondary amine (Scheme 21). Just one example was reported treatment with lithium naphthalenide gave the pyrrolidine product, predominantly as the cis isomer. 

The species which are unknown and have not been identified as one of the major chemical lump such as alkanes, phenols and aromatics are lumped together as unidentified. However, the species in this lump include saturated and unsaturated cycloalkanes with or without side chains, which resembles the naphthenes, a petroleum refinery product group. A number of well known species in coal liquid are not mentioned in this lumping scheme. Such as heterocyclic compounds with sulfur, nitrogen or oxygen as the heteroatom, and other heteroatora containing species. Some of these compounds appear with aromatics (e.g. thiophenes, quinolines) and with phenols (e.g. aromatic amines), and most of them are lumped with the unidentified species lump. 

In general, the reaction of unsaturated 5(4//)-oxazolones 497 with nitrogen nucleophiles effects ring opening to give the corresponding unsaturated acylamino amides 498 (Scheme 7.158). Depending on the nucleophile, for example, amines, hydrazines, oximes, and so on, the products obtained can be cyclized and this process allows the synthesis of a wide variety of new heterocyclic compounds. 

Reaction of unsaturated 5(4//)-oxazolones with bis(nucleophiles) opens the way for the preparation of diverse heterocyclic compounds depending on the nucleophilic atoms of the reagent. First, if we consider nitrogen-containing bis(nucleo-philes), the reaction of anthranilic acid with unsaturated oxazolones 550 gives rise to substituted 3,l-benzoxazin-4-ones 551 (Scheme 7.174). " °... 

Most of the heterocycles are known hy their trivial names, e.g. pyridine, indole, quinoline, thiophene and so on. However, there are some general rules to he followed in a heterocycle, especially in the use of suffixes to indicate the ring size, saturation or unsaturation as shown in the following table. For example, from the name, pyridine, where the suffix is -ine, one can understand that this heterocyclic compound contains nitrogen, has a six-memhered ring system and is unsaturated. 

The main aim of this monograph is a comprehensive review and organization of the known literature data devoted to the reactions of o,/3-unsaturated ketones, their synthetic equivalents and their precursors utilized in the synthesis of nitrogen-containing heterocycles. The book is separated into four chapters and an Addendum, and contains nearly 900 literature references. Each chapter describes the synthesis and chemical and other interesting properties and features of certain classes of heterocyclic compounds. 

Many of the chiral selenium electrophiles have also been employed in cyclization reactions. Various internal nucleophiles can be used and access to different heterocycles is possible. Not only oxygen nucleophiles can be used for the synthesis of heterocyclic compounds, but also nitrogen nucleophiles are widely employed and even carbon nucleophiles can be used for the synthesis of carbacycles with new stereogenic centers. Oxygen nucleophiles have been widely used and some selected examples of selenolactonizations of unsaturated acids 50 and 52 and seleno-etherifications of unsaturated alcohols 54 and 56 are shown in Scheme 10. 

Oxaziridines and oxazirines are the smallest heterocyclic compounds having three electronegatively different oxygen, nitrogen, and carbon atoms in a three-membered ring system. Oxaziridines are saturated molecules, whereas oxazirines are unsaturated as shown by the general structures 1 and 2. 

The ixeparatirai of many unsaturated heterocyclic compounds can be achieved via rDA processes. The vast majority of these compounds are either oxygen or nitrogen containing heterocyclics, preparation of which is most often accomplished by the expulsirai of an ethylene or a butadiene moiety. a-Methylene-oxetane (175a) and p-methyleneoxetane (175b) are obtained by a rDA process from the anthracene cycloadducts. 

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