Azodicarboxylic ester adducts

Similarly, no systematic study of the IR spectra of the pyridopyridazines has been recorded, but the spectra of the [2,3-d] derivatives have been discussed <68AJCl29l). The diones of this series have also been studied <69MI21501), and IR used to distinguish between the structure (303) and the possible isomeric formulation (304) <74JHC35l). The IR spectra of some of the azodicarboxylic ester adducts <79X2027) have been recorded, whilst in the benzo fused systems some problems with the structure of acyl derivatives in the pyridazino[4,5-6]quinoline series have been resolved with the help of IR spectroscopy <71BSF906, 72BSF1588). 

Amongst miscellaneous UV spectra recorded are those of alkylthio adducts of pyrido[3,2-c]pyridazine (78KGS1272), various pyrido[3,4-d]pyridazines (57AC(R)728) and several vinyl-pyridine-azodicarboxylic ester adducts (79T2027, 79KGS639). 

In common with other azodicarboxylic acid derivatives, the uses of 4-phenyl-l,2,4-triazoline-3,5-dione are many. It undergoes a Diels-Alder reaction with most dienes11-14 and is, in fact, the most reactive dienophile so far reported.15 16 As with the formation of all Diels-Alder adducts the reaction is reversible, and in the case of the adduct with 3-j3-acetoxy-17-cyano-5,14,16-androstatriene, the reverse reaction can be made to proceed under especially mild conditions.14 An instance has also been reported of the dione photochemically catalyzing other retro Diels-Alder reactions.17 Along with the proven use of azodicarboxylic ester,18-18 the dione should be potentially important in the preparation of strained ring compounds. 

Azodicarboxylic esters are excellent dienophiles and they can also add to electron-rich double bonds as heterodienes. Adducts of both types have been used as intermediates in the synthesis of amino sugars. 

Ketone silyl enol ethers react with derivatives of diacyl azo compounds at room temperature245 or on heating242,243 (see also Eq. 82) as well as enantio-selectively under the influence of silver trifluoromethanesulfonate and BINAP (Eq. 93)244 or copper bis(oxazoline) complexes (Eq. 94). The latter is proposed to proceed via a formal hetero Diels-Alder adduct.252 Ketones themselves react with azodicarboxylic esters either thermally246,389,390 or in the presence of potassium carbonate390 but yields are low. Higher yields can be achieved with LDA,391 394 (see also Eq. 88), LiHMDS,395,396 or KOBu-r325 as the bases. Aryl diazonium... 

Various azodicarboxylate esters have been used extensively as dienophiles.129 Several representative examples of this type of cycloaddition are listed in Table 6-III.33-40 As mentioned above, these reactions appear to be concerted processes that retain the 1,3-diene configuration in the adducts.303 The more bulky esters tend to react more slowly with dienes. Thus, dimethylazodicarboxylate reacts 5-6 times more rapidly with cyclopentadiene than does the ethyl ester,423 whereas the fert-butyl compound reacts sluggishly.42b... 

Pyridazine derivatives are also obtained by [4+2] cycloadditions. For instance, the tetrahydropyridazines 15 are produced by a Diels-Alder reaction from 1,3-dienes with azodicarboxylic ester. The pyridazines 17 are produced by addition of alkynes to 1,2,4,5-tetrazines followed by a retro-DiELS-Alder reaction of the adducts 16 with N2 elimination ... 

Without additional reagents Azodicarboxylic acid ester adducts 1-Aminohydrazines from tert. amines... 

Azodicarboxylic acid ester adducts Hydrazines by substituting addition... 

Diethyl azodicarboxylate forms normal adducts with 2,3-dimethylbutadiene and with ethyl sorbate however, it is not a very good dienophile, presumably because it exists in the fraws-configuration. The sterically hindered diene 254 adds the ester to give mainly the ene product 255 (equation 137) and even cyclohexa-1,3-diene undergoes an analogous... 

The cycloadducts 257 of esters of azodicarboxylic acid to 2,7-dimethyloxepin undergo a spontaneous Claisen rearrangement to form the dihydrocyclopropapyridazines 258 (equation 139)132. Homofulvenes 259 (R1, R2 = HorMe) react with dimethyl azodicarboxylate to form rearranged adducts 260 (equation 140)133. 

Scheme 6.81 Transformation of one adduct prepared from the 64-catalyzed asymmetric addition of a-substituted P-keto esters to di-tert-butyl azodicarboxylate (a-hydrazination) into the corresponding oxazolidinone amino acid derivative.

Thiolesters. These esters are easily obtained by addition of an alcohol and then t h iolacetic acid to the preformed adduct of P(C6H 5)3 and diisopropyl azodicarboxylate in THF (equation I). The reaction is accompanied by inversion of configuration.5... 

As l,2,4-triazole-3,5-dione (PTAD) is a stronger dienophile than acetylenic esters, more facile formation of the Diels-Alder cycloadducts was expected. But because it cannot behave as a diene in a reaction with alkynes such as diethyl azodicarboxylate, the formation of dihydrooxadia-zines is excluded. In spite of these characteristics, no Diels-Alder adducts were obtained in the reaction of l-phenyl-4-vinylpyrazole with PTAD in acetone at -80°C and 2,2-dimethyl-4(l-phenylpyrazol-4-yl)-8-phenyl-l,6,8-triaza-3-oxabicyclo[4.3.0]nona-7,9-dione 277 was obtained as a major product. The isolation of the tetrahydrooxadiazine 277 indicates that the 1,4-dipole 278 was formed and trapped with acetone. 

In the methodology developed by Oppolzer and Moretti18, closely resembling the Gen-nari, Colombo and Bertolini procedure15, the crude ketene silyl acetals 7, derived from the chiral esters 6, are reacted with di-tm-butyl azodicarboxylate (DBAD) to yield the adducts 8, and, via 9, the amino acids 10. 

Recently, enhanced ene reactivity was demonstrated for the bis(2,2,2-trichloroethyl) ester as compared with diethyl azodicarboxylate21. The use of this azodicarboxylate permitted the transformation of the adducts to amines to be accomplished under relatively mild conditions. 

Use of cyclopentene, frans-hex-3-ene and frans-oct-4-ene afforded the ene adducts in good yield with a diastereomeric excess of 86 14 in each case. The diastereoselectivity observed using di-(—)-( / ,25)-2-phenyl-l-cyclohexyl diazenedicarboxylate as a chiral azo-enophile offered a significant improvement over the use of di-(-)-menthyl azodicarboxylate where the level of asymmetric induction achieved in Lewis acid-mediated ene reactions with simple alkenes was not impressive. Moreover, it proved difficult to cleave the N-N bond in the menthyl ester azo-ene adducts whereas sodium/liquid ammonia was used to smoothly cleave the N-N bond in the diacylhydrazine adducts formed using di-(—)-(l/ ,25)-2-phenyl-l-cyclohexyl diazenedicarboxylate as azo-enophile. 

New Diels-Alder adducts of thebaine with aromatic nitroso-compounds of structure (118 R = H, Me, Cl) have been prepared. These are unstable and can be hydrolysed to 14-aryIhydroxylaminocodeinones (119), which can be reduced to derivatives of the hitherto inaccessible 14-aminodihydrocodeinone (120). The base (119 R = H) is susceptible to base-catalysed displacement of the oxide bridge, the product being the 5,14-bridged thebainone derivative (121). ° The reaction between thebaine and excess of ethyl azodicarboxylate involves Diels-Alder addition and addition of the N-CH3 group to a second molecule of azo-ester. The primary product (122) has not been isolated pure, but yields ethyl hydrazodicarboxylate and the substituted codeinone (123) on hydrolysis. ... 

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