Oximes heterocycle syntheses

The electrophile-induced cyclization of heteroatom nucleophiles onto an adjacent alkene function is a common strategy in heterocycle synthesis (319,320) and has been extended to electrophile-assisted nitrone generation (Scheme 1.62). The formation of a cyclic cationic species 296 from the reaction of an electrophile (E ), such as a halogen, with an alkene is well known and can be used to N-alkylate an oxime and so generate a nitrone (297). Thus, electrophile-promoted oxime-alkene reactions can occur at room temperature rather than under thermolysis as is common with 1,3-APT reactions. The induction of the addition of oximes to alkenes has been performed in an intramolecular sense with A-bromosuccinimide (NBS) (321-323), A-iodosuccinimide (NIS) (321), h (321,322), and ICl (321) for subsequent cycloaddition reactions of the cyclic nitrones with alkenes and alkynes. 

Nitrile oxides have been used extensively in heterocyclic synthesis. They are readily generated from oximes, using sodium hypochlorite under phase-transfer conditions, in high yields. They are versatile, lending themselves to one-pot procedures and reaction in situ with dipolarophiles. Lee discusses a wide variety of their reactions, notably the intramolecular reaction in which the benzopyran derivatives (48) are formed in yields that are more than double those previously reported. 

Abele E, Lukevics E (2000) Recent advances in the synthesis of heteroeyeles from oximes. Heterocycles 53(10) 2285-2336... 

As discussed in Chapter 6, nitro compounds are converted into amines, oximes, or carbonyl compounds. They serve as usefid starting materials for the preparation of various heterocyclic compounds. Especially, five-membered nitrogen heterocycles, such as pyrroles, indoles, ind pyrrolidines, are frequently prepared from nitro compounds. Syntheses of heterocyclic compounds using nitro compounds are described partially in Chapters 4, 6 and 9. This chapter focuses on synthesis of hetero-aromadcs fmainly pyrroles ind indolesi ind saturated nitrogen heterocycles such as pyrrolidines ind their derivadves. 

The concept of the use of dilithio reagents for the preparation of heterocyclic systems has been extended to the synthesis of 2-isoxazolin--5-ones10 by carboxylation of a dilithio oxime, followed by eyolin-zation, and the synthesis of pyrazoles from dilithiophenylhydrazones and trilithiothiohydrazones.11 12... 

Scheme 19 Synthesis of different heterocycles from resin-bound intermediate sulfonyl-oximes...

Main Rearrangements of BENA In previous Sections (3.5.4.1. and 3.5.4.2.), a-hydroxy oximes (503) and their bis-silyl derivatives (504) were considered as undesired by-products, formed in the synthesis and chemical transformations of BENA. The aim was to minimize the amount of these impurities. On the other hand, oximes (503) are convenient precursors of various useful products, such as p-amino alcohols (530), amino acids (531), a-hydroxycarbonyl compounds (532) and various heterocyclic systems (533). 

Oximes 28 are interesting precursors to / -amino acids, as well as different heterocyclic systems, so it is advantageous to develop the synthesis of the oximes 28 maximizing the side process shown in Scheme 20. This problem was solved in the earlier paper, which dealt with the double silylation of 26 with MesSiOTf/EtsN, but the yields of target derivatives were modest as a rule. ... 

The preparation of oximes from olefins is a valuable approach for the synthesis of nitrogen-containing compounds such as amino acids and heterocycles. Okamoto and colleagues have reported that a catalytic reduction-nitrosation of styrenes 31 with ethyl nitrite and tetrahydroborate anion by the use of bis(dimethylglyoximato)cobalt(II) complex afford the corresponding acetophenone oximes 32 (Scheme 23). 

Diketo oxime 43 (Scheme 27) find extensive use in organic synthesis. These compounds are useful building blocks in five-membered heterocyclic chemistry. These oximes can be used for the synthesis of pyrroles , thiazoles , oxazoles and pyrazoles . The diketo oxime 43 was synthesized in high yield by addition of an aqueous solution of sodium nitrite to a 0°C solution of 1-benzoylacetone 42 in AcOH . ... 

Nitrile oxides are widely used as dipoles in cycloaddition reactions for the synthesis of various heterocyclic rings. In order to promote reactions between nitrile oxides and less reactive carbon nucleophiles, Auricchio and coworkers studied the reactivity of nitrile oxides towards Lewis acids. They observed that, in the presence of gaseous BF3, nitrile oxides gave complexes in which the electrophilicity of the carbon atom was so enhanced that it could react with aromatic systems, stereoselectively yielding aryl oximes 65 and 66 (Scheme 35). ... 

Sulfahydantoins 87 and 88 are analogues of hydantoins and provide heterocyclic scaffolds with a great potential for the construction of bioactive compounds. A total of 28 derivatives, with crude purity generally higher than 85%, were prepared by parallel synthesis using an oxime resin as a solid support (Scheme 46) . The results constitute the first report of successful Mitsunobu reactions and reductive alkylations on the oxime resin. 

Oximes and their derivatives are widely used in organic synthesis. A number of reviews are devoted to the chemistry and biological activity of oximes and their derivatives The synthesis, reactions and biological activity of oximes containing a heterocyclic substituent, e.g. furan and thiophene", indole and isatin, pyridine, pyrrole, quinoline and five-membered heterocycles with two heteroatoms have been reviewed. 

Synthesis of heterocycles from amino amide oximes has been described. Recently we have reviewed the synthesis of oximes, oxime 0-ethers and esters, and also the synthesis of heterocycles from oximes covering the literature data published in 1990-1999 . 

Although some of these papers discuss also the synthesis of heterocyclic compounds, no general reviews on the synthesis of heterocyclic compounds from oximes and their derivatives have been published. 

II. SYNTHESIS OF HETEROCYCLIC COMPOUNDS FROM OXIMES A. Three-membered Rings... 

Synthesis of novel bicyclic heterocyclic systems involving aziiidine ring formation has been described. The sodium salts of tosylhydrazones 11 decomposed by heating in benzene and gave aziridinopyrroloindoles 12 in yields up to 73% (equation 5) . Intramolecular cyclization of oxime ether 13 in the presence of base (for example, DBU) in acetonitrile afforded aziridinopyrrolidine 14 in yields up to 51% (equation 6) °. 

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