Methyl azodicarboxylates

The mesoionic 4,5-diphenyl-l,3,4-thiadiazolium-2-thiolate (114) reacts with methyl azodicarboxylate to yield the azothiadiazole (115) and not the tetrazine betaine (116) as previously claimed. Compound (115) can also be prepared from 2-amino-5-phenyl-l,3,4-thiadiazole and nitrosobenzene (71CC837). 

It has been learned that a sample of methyl azodicarboxylate [Org. Synth., Coll. Vol. 11/1963, 411] violently decomposed during a distillation using an electrically heated mantle as a source of heat. 

Tests show that either methyl or ethyl azodicarboxylate can be detonated by shock or heat (C. S. Sheppard, H. N. Schack, and O. L. Mageli, U.S. Patent 3, 347, 845 [1967]), Methyl azodicarboxylate is far more easily detonated than the ethyl ester. Hence, since the chemical properties of the two esters are similar, ethyl azodicarboxylate is almost always the preferred reagent. 

Lastly, phthaloyl-protected (R)-alanine 112 is formed in high yield by reaction of 2 with phthalimide [40]. Recently, polystyrene-supported methyl azodicarboxylate has been used as a replacement for the soluble dialkyl azodicarboxylates in the Mitsunobu reaction [41]. Yields generally are not as high as in the classical reaction (e.g., 2 112, 45% yield), but, purification can be expedited simply by filtration of the nonexplosive resin. 

Treatment of the hydroxy acid 15 with methyl azodicarboxylate resin 17 yielded lactone 16 in 42% yield.21 The comparable reaction with soluble azodicarboxylate gave 16 in 8% only (Scheme 1.6.6). 

A further development of the method by immobilization of DEAD effects an easily separable (insoluble) and non-explosive reagent in Mitsunobu reactions. The methyl azodicarboxylate reagent immobilized on polystyrene 1742 functions well in Mitsunobu reactions and gives yields comparable to those obtained with soluble DEAD [1279]. Diphenylcarbodiimide was obtained in 41% yield. 

The other main source of various pyridopyridazines from pyridines are the [4 + 2] cycloaddition reactions, already mentioned (Section 2.15.8.3), between vinylpyridines and azodicarboxylic esters (79T2027, 79KGS639) or triazolidinediones e.g. 78KGS651). 2-Vinyl-pyridines gave reduced pyrido[3,2-c]pyridazines (370), 4-vinylpyridines gave [3,4-c] analogues, whilst 2-methyl-5-vinylpyridine furnishes a mixture of the [2,3-c] and [4,3-c] compounds. Yields are low, however, and these remain curiosities for practical synthetic purposes. 

To prepare fervenulin 4-oxides 12 or toxoflavine 4-oxides 146, it is convenient to use the reaction of l,3-dimethyl-2,4-dioxopyrimidin-6-yl hydrazone 147 or N-(3-methyl-2,4-dioxopyiimidin-6-yl) iV-methylhydrazone 148 with potassium nitrate in acetic acid [75CPB1885,76CPB338,76JCS(CC)658,82JHC1309,93CPB362]. Diethyl azodicarboxylate can be used instead of potassium nitrate [76JCS(P1 )713]. 

Cydization of P-hydroxy-a-amino esters under Mitsunobu reaction conditions is an alternative approach to aziridine-2-carboxylic esters [6b, 13-16], In this case the P-hydroxy group is activated by a phosphorus reagent. Treatment of Boc-a-Me-D-Ser-OMe 13 (Scheme 3.5) with triphenylphosphine and diethyl azodicarboxylate (DEAD), for example, gave a-methyl aziridinecarboxylic acid methyl ester 14 in 85% yield [15]. In addition to PPh3/DEAD [13b, 15], several other reagent combi-... 

A very mild procedure for converting alcohols to iodides uses triphenylphosphine, diethyl azodicarboxylate (DEAD), and methyl iodide.24 This reaction occurs... 

The 3-methyl- and 3-phenyl-l,2,3-oxadiazolinium salts 96 and 97 are capable of oxidizing thiols to disulfides <1995MI817>. New dihydro-1,2,3-benzoxadiazoles, prepared by the reaction of 1,2-benzoquinones with diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) in the presence of triphenylphosphine (Section 5.03.9.4), have been shown to undergo catalytic hydrogenolysis to give phenols (Equation 12) <20050L5139>. 

Wang resin was purchased from Advanced ChemTech (1% DVB, 0.70mmol/g substitution, 100-200 mash, Cat. SA5009). Anhydrous tetrahydrofuran (THF), A/A-dimcthyl-formamide (DMF), methanol, dichloromethane, pyridine, 1,1 -carbonyldiimidazole (CDI), piperazine, homopiperazine, trans-1,4-diaminocyclohexane, 4-(dimethylamino)pyridine (DMAP), succinic anhydride, diglycolic anhydride, 3-methyl-glutaric anhydride, 2-aminophenol, 2-amino-p-cresol, 2-amino-4-tert-butyl phenol, /V-methylmorpholine (NMM), triphenylphosphine, diethyl azodicarboxylate (DEAD), and trifluoroacetic acid (TFA) were purchased from Aldrich Chemical Company, Inc. and used without further purification. PyBOP was purchased from Novabiochem. 

Coupling of excess (Z)-l,2-dichloroethene (217) with propargyl alcohol first led to the enyne 218, which, when subjected to a second Pd-catalyzed coupling step with trimethylsilylacetylene, provided the mixed diacetylene 219. With all carbon atoms assembled, the allene function was generated by first producing the (unprotected) hydrazine derivative 220, which on treatment with either diethyl azodicarboxylate (DEAD) or 4-methyl-l,2,4-triazoline-3,5-dione (MTAD) under anaerobic conditions at 0 °C yielded the hydrocarbon 27. According to mechanistic studies, the latter process leads first to a mixture of ( )- and (Z)-diazenes. Sigmatropic elimination of... 

The hydroxymethyl and carboxyl group of Ser can participate in pyrazole-ring formation, as shown in the transformation of A -protected L-Ser with the Mitsunobu reagent into a /3-lactone which afforded the N-protected serine hydrazide upon treatment with methyl hydrazine. Cyclization to 25 was achieved by diisopropyl azodicarboxylate (DIAD) and TPP [90H(31)79]. 

Additionally, uracil 6-iminophosphorane, isocyanate, and o-methyl-e-caprolactim ether join to form the intensely yellow pyrimido[4 5 4,5] pyrimido[6,l-n]azepine (360), as shown in Scheme 130. Upon ring closure, methanol is spontaneously eliminated. Diethyl azodicarboxylate affords with the other components pyrimido[4,5-e][l,2,4]triazoline (361), which is closely related to the alkaloid isofervenuline. The imidazo[5, -/][ ,2,4]tria-zine (362) results in a known Michael-type rearrangement sequence by treatment with diethyl acetylenedicarboxylate (86JOC149, 86JOC2787) in this latter case, the Michael-type addition occurs much faster than the expected three-component reaction [93H(35)1055]. 

This work has been extended from aryl and alkyl substituted systems (42) (R = aryl, alkyl) to analogues where R is an amino group, so giving access to synthetic equivalents of the nonstabilized amino nitrile ylides (45). Adducts were obtained in good-to-moderate yield with A-methyhnaleimide (NMMA), DMAD, electron-deficient alkenes and aromatic aldehydes (27,28), and with sulfonylimines and diethyl azodicarboxylate (29). Similarly the A-[(trimethylsilyl)methyl]-thiocarbamates (46) undergo selective S-methylation with methyl triflate and subsequent fluorodesilylation in a one-pot process at room temperature to generate the azomethine ylides 47. 

Avalos and co-workers (220-228) extensively investigated the 1,3-dipolar cycloaddition chemistry of 2-aminothioisomiinchnones with both acetylenic and olefinic dipolarophiles. For example, sugar derivatives of the mesoionic imi-dazo[2,l-Z7]thiazolium-3-olate system react regioselectively with a variety of acetylenic dipolarophiles [DMAD, diethyl azodicarboxylate (DEAD), methyl propiolate, ethyl phenylpropiolate] to give the corresponding imidazo[l,2-a]pyr-idin-4-ones (e.g., 323) following sulfur extrusion from the not isolable cycloadducts (220). Similarly, these thioisomtinchnones react with diethyl azodicarboxylate and arylisocyanates in the expected fashion (221), and also with aryl aldehydes to form episulfides (222). 

The betaines 170 (R = Me, 2,4-dinitrophenyl) are reactive 1,3-dipolar-species. With electron-deficient olefins they give tricyclic adducts (172). Acetylenes and diethyl azodicarboxylate give similar adducts (173 and 174) (Scheme 7). Menschutkin methylation of 172 gives the methiodides (175) which undergo Hofmann elimination to 2-dimethylamino-6,7-benzo-tropones (177) (Scheme 7). The benzocycloheptadienones (176) are not... 

The reaction of indolizines with dialkyl acetylenedicarboxylates in the presence of a dehydrogenating catalyst leads to 1,2-dicarbalkoxycycl-[3,2,2]azines.22 23 Methyl phenylpropiolate may be used instead, although attempts to effect reaction between indolizine and certain other dienophiles including diphenylacetylene, diethyl azodicarboxylate, and 1,3-cyclohexadiene were unsuccessful. Hydrolysis of the diesters yielded the corresponding acids. Subsequent decarboxylation proceeded in high yield using copper chromite in quinoline [Eq. (5)]. 

Much work has been done on configuration and conformation, e.g. of 2-methoxy-2-oxo-4,5-diphenyl-l,3,2-dioxaphospholanes with 170 and lsO labelled reagents (81CC245). A large number of 2-dimethylamino-l,3,2-dioxaphospholanes or 3-methoxy-2-methyl-l,3,2,-oxazaphospholanes are mentioned in a recent publication, in which spiro compounds of the general structure (108) were prepared by addition to diethyl azodicarboxylate (equation (69)) (80PS(8)147>. 

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