Addition reactions 1,6-dipolar

An independent synthesis of 120 was achieved by O-benzylation of 2,5-anhydro-D-gluconamide33 however, undesirable side-reactions made this alternative approach impractical. Compound 120 was subsequently transformed into a C-/3-D-arabinofuranosylated heterocycle by way of a 1,3-dipolar addition-reaction of the 1-diazo intermediate 122 to dimethyl acetylenedicarboxylate (see Section IV,2). 

Several C-/3-D-pentofuranosylpyrazoles are known, but most of these derivatives have been prepared and utilized as intermediates in the synthesis of 3-glycosylpyrazolopyrimidines, such as the for-mycins and their analogs. Among these are the synthetic intermediates 246, 250, 257, and 280, which, for the most part, were obtained by 1,3-dipolar addition reactions. 

Further studies on 1,3-dipolar addition reactions of diazophosphonates have been recorded,122 and work on 2-diazo-l-hydroxyalkylphosphonates also continues.123 The ester (155 R = H) reacts with esters of acetylenedicarboxylic acid without liberation of nitrogen to give stereoisomeric C-phosphorylated pyrazolines, which can be decomposed with both phosphorus-carbon and carbon-carbon bond fission, affording mixtures containing dimethyl acetylphosphonate, dimethyl hydrogen phosphonate, and tri(alkoxycarbonyl)pyrazolines. In the reaction between the same diazophosphonate and diazomethane, the latter conceivably acts as a basic catalyst for proton transfer in a series of steps which includes phosphonate-phosphate isomerization. The importance of a labile proton is demonstrated by the fact that the ester (155 R = Me) does not react in the manner described above. 

Yields from 1,3-dipolar addition reactions with pyridinium ylides are enhanced by the addition of phase-transfer catalysts [60]. The ylides are produced in situ under basic two-phase conditions and react at room temperature with acetylenic dipolarophiles. 

The 1,3-dipolar addition reaction of fullerene with diazo compounds is one of the most studied reactions in the early stage of the research on fullerene chemistry [7]. The reaction in solution first affords rather labile fulleropyrazoline derivative 26, which is readily converted to the so-called 5,6-open (a bond originally shared by five- and six-membered rings cleaved) fulleroid (27) or 6,6-closed (a bond shared by two six-membered rings remaining closed) methanofullerene derivatives (28) by heat (e.g., refluxing in toluene) or photoirradiation (UV light), respectively (Scheme 11) [7a]. 

Intramolecular Cycloadditions of Carbonyl Ylides W. Eberbach, J. Brokatzky and H. Fritz, Angew. Chem., Int. Ed. Engl., 1980, 19, 47-48. a,(3-Unsaturated Heteroatomic Compounds in 1,3-Dipolar Addition Reactions V. A. Galishev, V. N. Chistokletov and A. A. Petrov, Russ. Chem. Rev. (Engl. Transl.), 1980, 49, 880-892. 

Dipolar addition reactions of suitably substituted 1,3-dipoles to dipolarophiles offer a wide range of utility in the synthesis of fused heterocyclic ring systems (63AG(E)565). The... 

The meta-bridging cyclizations of azines with bifunctional nucleophiles usually occur in two steps and differ substantially in that respect from the 1,3-dipolar addition reactions performed on 3-hydroxypyridinium salts, which also result in meta-bridged adducts (Scheme 55) (76JCS(P1)2285). 

Cycloadditions [40] Perfluoro-2-butyne is a highly reactive dienophUe and many [4 + 2] cycloaddition and 1,3-dipolar addition reactions involving this alkyne have been reported (Table 7.20). Moreover, [2 + 2] additions with hydrocarbon alkenes are possible (Table 7.20). 

The great synthetic potential of the general 1,3 dipolar addition reaction developed by Huisgen et has stimulated interest in new 1,3 dipolarophiles, e.g. the... 

Alkynes undergo 1,3-dipolar addition reactions with organic azides to form triazolesCommonly, hydrazoic acid additions to alkynes also give triazoles and this aspect of their chemistry has been... 

Anodic oxidation of benzylidenephenylhydrazine gives diarylnitrileimine, which may react with suitable dienophiles in a 1,3-dipolar addition reaction. Pyridine [130], some alkenes, and iV-heterocycles [131] may act as dienophiles with formation of substituted 1,2,4-triazoles (XL) or pyrazolines ... 

The prodocts of [3 -f- 2] cycioadditions are five-member heterocyclic systems. A large body of information is available concerning the scope of 1,3-dipolar addition reactions and their mechanistic interpretation a detailed discussion is outside the realm of this book. 

Lemal et al. studies the 1,3-dipolar addition reaction of the Dewar thiophene with trifluoromethyl diazomethane. The cycloadduct shows reactions which are similar to those of the azide adducts (122) 126). 

The reactions of 2-aminobenzimidazoles have been reviewed <83S86l>. The compounds form Schiffs bases with carbonyl compounds, with isocyanates and isothiocyanates they give ureas and thioureas, they are subject to 1,3-dipolar addition reactions, and to the formation of carbamates on acylation and aroylation. When aminoimidazoles are acylated there is frequently competition between the annular and exocyclic nitrogen (see above). Add chlorides and anhydrides (soft) acylate the amino group chlorocarbonic acid esters (hard) are specific for the heteroatom <84CHE204>. When heated, the A -acyl products isomerize (Scheme 91). 

Treatment of synlanti mixtures of aldoximes (69) with allylboronates generates N-(homoallyl)hydrox-ylamines (70) in good yield (Scheme 6). - The anti oxime reacts faster than the syn isomer. N-(Ho-moallyl)hydroxylamines (70) have been converted to homoallylamines (71) (with iron(II) dihydrolipoate) and have been treated with aldehydes to generate highly functionalized nitrone intermediates (72) for use in 1,3-dipolar addition reactions. 

In summary, it appears that Reissert salts undergo 1,3-dipolar addition reactions with reactive acetylenic 1,3-dipolarophiles57-58 to give compounds of type 24 and undergo complex condensation-rearrangement reactions with olefinic dienophiles57-59 to give products of the type 25. 

Many enone systems readily undergo 1,3-dipolar addition reactions. This applies to steroids, as illustrated by the formation of the fused pyrazole 16-4 from reaction of the enone 16-2 with diazomethane. Pyrolysis of that pyrazole results in extrusion of nitrogen to leave behind a methyl group at position 1 (16-5). 

Recent examples of 1,3-dipolar addition reactions include the additions of aryl nitrile oxides, ethyl diazoacetate, or tert-buty azidoacetate to dialkyl (perfluoroalk-l-ynyl)phosphonates , and further reactions of the nitrilimine (520) have been reported. ... 

Indolizines, indolizidines, indoles, and other bicyclic or polycyclic compounds containing a fused pyrrole or pyrrolidine moiety often possess potent and useful biological activities. There have been several approaches to the preparation of fluorinated analogues of these heterocycles, mainly based on 1,3-dipolar addition reactions using fluorinated synthons either as the dipole or as the dipolarophile. Several examples of this strategy are given below. 

Dipolar addition reactions of iV-ylides with 2,2-difluorovinyl tosylate provides a convenient route to moderate yields of monofluorinated indolizines and related structures. A -Ylides derived from pyridinium, isoquinolinium, and bezimidazolium salts were generated in situ from halide salts (Fig. 3.31)7 ... 

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