Heterocycles as intermediates in organic

Polycyclic cage heterocycles as intermediates in organic synthesis 91SL43. 

Reactivity (General Topics, Reactions with Electrophiles and Oxidants, Reactions with Nucleophiles and Reducing Agents, Reactions toward Free Radicals, Carbenes, etc., Reactions with Cyclic Transition State, Reactivity of Substituents, Heterocycles as Intermediates in Organic Synthesis). 

Organomercury derivatives of heterocycles in synthesis 85MI12. Organosilicon and organotin derivatives of thiazole and oxazole as intermediates in organic synthesis 88G211. 

A variety of heterocyclic compounds have been derived from the condensation of aldehydes with a-amino acids. Imines 1 (Fig. 3) are often used as intermediates in organic synthesis and are the starting point for chemical reactions such as cycloadditions, condensation reactions, and nucleophilic additions. The formation of imines via condensation of amines with aldehydes was first adopted for the reductive alkylation of resin-bound amino acids [29-31]. Imines have now been used as synthetic intermediates in the generation of a range of heterocyclic combinatorial libraries. 

Heterocycles in organic synthesis , Meyers, A. I., Wiley-Interscience, New York, 1974 for a more recent article in the same vein see Five-membered heteroaromatic rings as intermediates in organic synthesis , Lipshutz, B. H., Chem. Rev., 1986,86, 795. 

The synthesis of heterocyclic compounds using transition metals and using heterocyclic compounds as intermediates in the synthesis of other organic compounds will bean additional feature of each volume. Pathways involving the destruction of heterocyclic rings will also be dealt with so that the synthesis of specifically functionalized non-heterocyclic molecules can be designed. Each volume in this series will provide an overall picture of heterocyclic compounds... 

Organophosphorus compounds are important intermediates in organic synthesis and have been widely used as pharmaceutical [1-6], agricultural [7], and chemical agents [8-14], Recently phosphorus heterocycles [15,16] have received considerable interest... 

The 5-oxazolones or oxazolin-5-ones are very interesting heterocyclic compounds that have been used as intermediates in the synthesis of a variety of organic molecules. Two structural classes are possible, the 5(27T)-oxazolones (or 3-oxazo-lin-5-ones) and 5(47T)-oxazolones (or 2-oxazolin-5-ones). These structures differ only in the position of the double bond. Apart from the presence of the heteroatoms (N and O), the carbonyl group and the double bond, the 2- or 4-position, respectively, can be saturated or unsaturated. The isomeric 5-oxazolones are... 

The chemistry and synthetic applications of oxazoles were first covered in 1986 in an comprehensive volume edited by I. J. Turchi (Volume 45 of The Chemistry of Heterocyclic Compounds series). In the meantime, the number of synthetic strategies directed toward oxazole assembly as well as the use of these versatile heterocycles as intermediates, catalytic ligands, and pharmaceutical building blocks has vastly increased. We felt that a supplement and update of oxazole chemistry would be welcomed by the international chemistry community, and we are delighted that Dr. Palmer and his colleagues have accomplished this onerous mission. This volume represents another outstanding service to the organic and... 

It is abundantly clear from the preceding discussion that dihalocyclopropanes are versatile intermediates in organic synthesis. Although a wealth of chemistry has already been uncovered, prospects remain bright for interesting developments in the future. Areas such as the application of dihalocyclopropanes in heterocyclic synthesis via carbene insertion into C—H bonds adjacent to heteroatoms, reactions of dihalocyclopropanes with organometallics and the synthetic applications of metallated derivatives deserve further exploration. The chemistry of difluoro-, diiodo- and mixed dihalo-cyclopropanes can be expected to attract some attention. Finally, other heteroatom-substituted cyclopropanes derived ftom dihalocyclopropanes will also invoke further investigation. 

Therefore, this review is mainly devoted to the application of electroorganic reactions to the synthesis of some key skeletons which are commonly found in natural alkaloids and some key intermediates which are useful materials for the formation of alkaloidal structures. The synthesis of some other nitrogen heterocycles which are usually not found in alkaloidal compounds will not be part of this review even though the structures are highly interesting as targets in organic synthesis. 

The HDA reaction allows for rapid access to chiral six-membered heterocyclic structures that serve as valuable intermediates in organic synthesis. The first highly enantioselective HDA reaction promoted by a chiral hydrogen bond donor was reported from the Rawal laboratory. While investigating the cycloaddition reactions of amino-siloxy diene 115, it was observed that this diene was exceptionally reactive to heterodienophiles, and underwent HDA reactions with various aldehydes at room temperature, even in the absence of any added catalyst (Scheme 6.14). Subsequent treatment of the intermediate cycloadducts (116) with acetyl chloride afforded the corresponding dihydro-4-pyrones (117) in good overall yields [101]. Further studies of this reaction revealed a pronounced solvent effect,... 

Enaminones are useful and widely used synthons in organic synthesis of alicyclic, aromatic and heterocyclic compounds. Frequently, it is assumed that enaminones are formed as intermediates in the synthesis of heterocycles. However, when they are not isolated, they are not considered in this article. Moreover, there are many examples of formal analogues of enaminones (e.g. aromatic or quinonoid compounds) as well as heterosubstituted derivatives4 which are also not discussed in the present chapter. 

E-3-alkoxyacryloyl chlorides are high potential intermediates in organic synthesis, especiaiiy for the preparation of various heterocycles, such as coumarins [Scheme 21] ... 

Mesoionic five-membered heterocycles are also an important group of heterocyclic compounds. These compounds are very useful intermediates in organic synthesis because they react as dipolar components in 1,3-dipolar cycloaddition reactions. They are photochemically isomerized to other dipolar compounds via Dewar-type intermediates. These dipolar compounds are converted to products different from those formed in the thermal reaction (118) U8). (Concerning this type of reaction, see ref.102).)... 

N-Acyliminium ions are versatile intermediates in organic synthesis they not only react with various nucleophiles such as electron-rich aromatic and heteroaromatic compounds but also undergo cycloaddition reactions with unsaturated compounds.It is especially noteworthy that N-acyliminium ions serve as electron-deficient 4t7 components in [4 + 2] cycloaddition with alkenes and alkynes. " This reaction serves as a useful method for the construction of heterocyclic rings containing a nitrogen atom. Acyclic structures containing amino and hydroxyl groups can also be synthesized from the initially formed cyclic compounds. 

One example of a successful application of solid-phase chemistry constitutes the highly versatile synthesis of quinazolinones 300/301 which efficiently combines an aza.-Wittig reaction with a multidirectional cyclisation cleavage. Iminophosphoranes were shown to be useful intermediates in organic synthesis, particularly for the preparation of different heterocyclic systems containing an endocyclic C,N double bond. In these cases, an aza-Mfrig-mediated anellation reaction was involved as the key step. 27-i29... 

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