Synthesis of various derivatives

Due to these procedures as well as to some other transformations, the a-azido oximes can be considered as efficient basic reagents in the synthesis of various derivatives of 1,2-disubstituted ethanes using readily available AN (431) as starting compounds. 

Numerous papers have been devoted to the synthesis of various derivatives of 2-pyridone, 4-pyridone, and aminopyridines based on enamines, di-enamines, dienediamines, and related compounds. For example, enamin-odiketones (153) can react with cyanoacetamide in tetrahydrofuran in the presence of sodium hydride with the formation of a substituted 3-cyano-2-... 

Nucleophilic substitution of halogens in the ring or in side chains have been used for the synthesis of various derivatives of tellurophene. The reaction of 2-iodotellurophene with thiols catalyzed by Cu(i) ions gives rise to 2-organylthiotellurophenes 13 in 77-90% yields (Equation 3) <2005TL2647>. 

Proton and, occasionally, carbon nmr spectra of thietanes are reported routinely in descriptions of the synthesis of various derivatives. Although an early proton nmr spectrum indicated identical chemical shifts for the a- and -protons of thietane, more recently the spectrum has been analyzed as an A4B2 system and additional chemical shifts (S Hj=3.43, = 3.17) and coupling con-... 

In recent years, nucleophilic addition reaction has been widely used for the synthesis of various derivatives of isomeric naphthyridines. For example, nucleophilic addition of indole to 1,5-, 1,6- and 1,8-naphthyridine derivatives in the presence of benzoyl chloride in toluene or DMF yields, depending on the temperature and reactant ratio, hydrogenated mono- (256-265) or fc-(3-indolyl)naphthyridines 259-264 (1985MI2, 1986KGS1218, 1986MI3). Hetarylation includes the in situ formation of /V-acyl heteroaromatic cations and the addition of nucleophiles to them. Aromatization of the N-acylated hydrogenated naphthyridine derivatives 259 and 264 on treatment with tetrachloroquinone affords the same compound, naphthyridine 265. 

The reaction of 2-amino-3-nitrosopyridines with compounds containing an activated methylene group permits unambiguous synthesis of various derivatives of pyrido[2,3-b]pyrazine. For example, the pyridine 58 reacts in the presence of sodium ethoxide with a variety of arylacetonitriles and cyanoacetic acid derivatives to provide various 2-substituted 3-amino compounds (59). " " Diethyl malonate reacts similarly to give the 2-carboxylic acid 60, its ester being presumably hydrolyzed in the alkaline reaction conditions. Ethyl acetoacetate yields the 2-acetyl-3-oxo compound 61, and acetylacetone ° provides the 2-acetyl-3-methyl compound 62. The latter condensation proceeds poorly in ethanolic sodium ethoxide, but heating the nitroso compound with acetylacetone under reflux in pyridine gives a 59% yield of the product 62. °... 

When we started our research in the late 1960s, the synthesis of various derivatives of imidazopyridines was seldom studied. 

Another triflate ester that recently has found growing application in organic synthesis is commercially available trimethylsilylmethyl trifluoromethanesul fonate. This powerful alkylating reagent can be used for the synthesis of various methylides by an alkylation-desilylation sequence A representative example is the generation and subsequent trapping by 1,3-dipolar cycloaddition of indolium methanides from the corresponding indole derivatives and trimethylsilylmethyl trifluoromethanesulfonate [108] (equation 54)... 

Perhydro derivatives of pyrido[l,2-7)][l,2]oxazines are frequently applied in the total synthesis of various alkaloids to control the stereochemistry, and pyrido[l,2-c][l,3]oxazines and [l,3]oxazino[3,4-u]quinolines were also used in the stereoselective syntheses of different alkaloids. Perhydropyrido[l,2-c][l,3]oxazines and their benzologs are formed form 2-(2-hydroxyethyl) piperidines and from their benzologs to justify the stereochemistry of 2-(2-hydroxyethyl) derivatives. Different optically active pipecolic acids can be prepared via 4-phenylperhydropyrido[2,l-c][l,4]oxazin-l-ones. 

Yosida et al. [41] found that p-t< rr-butylcalix[6]ar-ene can extract Cu from the alkaline-ammonia solution to the organic solvent. Nagasaki and Shinkai [42] described the synthesis of carboxyl, derivatives of calix-[n]arenes ( = 4 and 6) and their selective extraction capacity of transition metal cations from aqueous phase to the organic phase. Gutsche and Nam [43] have synthesized various substituted calix[n]arenes and examined the complexes of the p-bromo benzene sulfonate of p-(2-aminoethyl)calix[4]arene with Ni, Cu , Co-, and Fe. ... 

Unsolvated organomagnesium compounds have been recommended for the synthesis of organometallic derivatives of mercury, boron, aluminum, silicon, germanium, tin, phosphorus, arsenic, and antimony6-8 and have been used in procedures for the alkylation of aromatic rings and for the production of various polymerization catalysts.4 9... 

This is the most convenient preparation of 4 pyridinesulfonic add, a useful intermediate for the synthesis of various pyridine derivatives... 

The direct reductive amination (DRA) is a useful method for the synthesis of amino derivatives from carbonyl compounds, amines, and H2. Precious-metal (Ru [130-132], Rh [133-137], Ir [138-142], Pd [143]) catalyzed reactions are well known to date. The first Fe-catalyzed DRA reaction was reported by Bhanage and coworkers in 2008 (Scheme 42) [144]. Although the reaction conditions are not mild (high temperature, moderate H2 pressure), the hydrogenation of imines and/or enam-ines, which are generated by reaction of organic carbonyl compounds with amines, produces various substituted aryl and/or alkyl amines. A dihydrogen or dihydride iron complex was proposed as a reactive intermediate within the catalytic cycle. 

In addition, several S/S ligands were also investigated for the asymmetric hydrogenation of olefins. In 1977, James and McMillan reported the synthesis of various disulfoxide ligands, which were applied to the asymmetric ruthenium-catalysed hydrogenation of prochiral olefinic acid derivatives, such as itaconic acid. These ligands, depicted in Scheme 8.16, were active to provide... 

By using a mixture of ethyl acetate and D2O as solvent for hydrogenation, up to 75% deuterium is incorporated in the reduced product.13 This result indicates that the role of water here is not only as a solvent. Research on asymmetric hydrogenation in an aqueous medium is still actively being pursued. The method has been applied extensively in the synthesis of various amino acid derivatives.14... 

The spirobenzylisoquinoline 171b derived from berberine (15) (Section IV,A,1) was oxidized with m-chloroperbenzoic acid to the /V-oxide 389, which was treated with trifluoroacetic anhydride to afford dehydrohydrastine (370) in 56% overall yield (Scheme 71) through the Polonovski reaction (187). Holland et al. (188,189) reported the reverse reaction from dehydrophthalides to spirobenzylisoquinolines, namely, 370 was reduced with diisobutylalu-minum hydride to give a mixture of two diastereoisomeric spirobenzylisoquinolines 320 and 348 via the enol aldehyde. This reaction was applied to synthesis of various spirobenzylisoquinoline alkaloids such as (+)-sibiricine (352), ( + )-corydaine (347), (+ )-raddeanone (354), ( )-yenhusomidine (359), (+ )-ochrobirine (343), and ( )-yenhusomine (323). 

Dipolar addition to nitroalkenes provides a useful strategy for synthesis of various heterocycles. The [3+2] reaction of azomethine ylides and alkenes is one of the most useful methods for the preparation of pyrolines. Stereocontrolled synthesis of highly substituted proline esters via [3+2] cycloaddition between IV-methylated azomethine ylides and nitroalkenes has been reported.147 The stereochemistry of 1,3-dipolar cycloaddition of azomethine ylides derived from aromatic aldehydes and L-proline alkyl esters with various nitroalkenes has been reported. Cyclic and acyclic nitroalkenes add to the anti form of the ylide in a highly regioselective manner to give pyrrolizidine derivatives.148... 

The foregoing examples show that the nucleophilic attack to nitroarenes at the o>T/ o-position followed by cyclization is a general method for the synthesis of various heterocycles. When nucleophiles have an electrophilic center, heterocyclic compounds are obtained in one step. Ono and coworkers have used the anion derived from ethyl isocyanoacetate as the reactive anion for the preparation of heterocyclic compounds. The carbanion reacts with various nitroarenes to give isoindoles or pyrimidines depending on the structure of nitroarenes (Eqs. 9.56 and 9.57).89 The synthesis of pyrroles is discussed in detail in Chapter 10. 

CHEC-II(1996) comprehensively outlines the most commonly used synthetic approaches applied to these types of bicyclic compounds of phosphorus, arsenic, antimony, and bismuth <1996CHEC-II(8)863>. The six classes of compounds listed in this section have received considerable attention over the review period and as such the principal synthetic methods for these compounds are discussed. Schoth et al. <2000CCR101> have reviewed the use of fluorinated 1,3-diketones, 2-trifluoroacetylphenols, and their derivatives in the synthesis of phosphorus compounds. Included in this review is the use of these reagents for the synthesis of various [3.3.1] nonfused and [3.3.0] fused phosphorus bridgehead bicyclic systems. 

It has been previously shown that selective etching of carbides is an attractive technique for the synthesis of various carbon structures. Carbon produced by extraction of metals from carbides is called carbide-derived... 

Ring-closing reactions promoted by mercuric salts are valuable transformations which find an increasing use in the total synthesis of various natural products.130-140 Several examples of solvomercurations demonstrating the applicability of these transformations to the synthesis of natural product precursors are presented in Table 2. Piperidines (entry a), 141 pyrans (entries b-d), 142-144 and furans (entries e, f)14S>146 have been obtained in good yields and diastereoselectivity. These derivatives serve as starting materials for various natural products and can be demercu-rated under reducing conditions.147... 

When the alkynyl substrate possesses a nucleophilic functionality, intramolecular solvomercuration reactions can sometimes be observed. These reactions, which result in the formation of a heterocycle, have been used in the total synthesis of natural products. For example, reaction of 114 with Hg(OAc)2 affords the benzofuran derivative 115, which is an important intermediate for the synthesis of various neolignans (Equation (42)).154 155... 

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