Azodicarboxylic acid rings with

The photocycloaddition of arylazirines with a variety of multiple bonds proceeds in high yield and provides a convenient route for the synthesis of five-membered heterocyclic rings. Some of the dipolarophiles include azodicarboxylates, acid chlorides, vinylphosphonium salts and p-quinones. 

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. 

The photochemical addition of 2H-azirines to the carbonyl group of aldehydes, ketones and esters is completely regiospecific (77H143). Besides the formation of the isomeric oxazolines 18 from 3 and ethyl cyanoformate, there is also formed the imidazole 19 from addition to the C = N in the expected regioselective manner. Thioesters lead to thiazolines 20, while isocyanates and ketenes produce heterocycles 21 (Scheme 4). The photocycloaddition of arylazirines with a variety of multiple bonds proceeds in high yield and provides a convenient route for the synthesis of five-membered heterocyclic rings. Some of the dipolarophiles include azodicarboxylates, acid chlorides, vinylphospho-nium salts and p-quinones. 

Stoodley developed an asymmetric synthesis of (5A)-2,3,4,5-tetrahydropyridazine-3-carboxylic acid (see Section 8.01.6.4). The ring construction was achieved via cycloaddition of dienes 295 bearing a tetraacetyl /3-D-glucopyranosyl moiety for chiral induction with azodicarboxylates (Equation 73) <1999J(P1)2591>. 

The synthetic potential of a simple method for the direct introduction of nitrogen into the 5-position of the pyrimidine ring is illustrated by the synthesis of 1,3-dimethyluric acid (15) from 1,3-dimethyluracil-6-amine by reaction with diethyl azodicarboxylate, reduction to 5-[(ethoxycarbonyl)amino]-l,3-dimethyluracil-6-amine, and thermal ring closure. "... 

Diethyl azodicarboxylate can join two ring-carbon atoms through a nitrogen atom. An alternative is to treat the compound with nitrous acid so as to connect the two rings through an iV-oxide function. Both methods can give good yields. 

There are efficient ways in which to use starting materials that have the carboxylic acid component already installed on both heteroatoms conversion to bis(silyloxy) derivatives, or simply heating with p-toluenesulfonic acid. An excellent route to mono-acylated precursors utilises mixed anhydrides. A very mild method for the dehydrative ring closure of ortfto-hydroxyarylamino-amides utilises typical Mitsunobu conditions - triphenylphosphine and diethyl azodicarboxylate. ... 

Oxadiazines are prepared by cyclodehydration of iV-phenacyl-iV -acylhydrazines under acid conditions (Section 6.17.7.1.1). 5,6-Dihydro-4/7-1,3,4-oxadiazines are available by [4 -I- 2] cycloaddition of vinyl heterocycles with azodicarboxylates (Section 6.17.7.2.2(i)) and by ring expansion of... 

Cycloadditions. Addition of diethyl azodicarboxylate or related derivatives to polyenes proceeds easily. Further examples of this important route are shown in Scheme 12. The ease with which these adducts may undergo Claisen rearrangement has been further studied. " Rearrangement is facilitated by ring strain and also by electron release from N-substituents (48) is stable even at elevated temperatures. The rearrangement is acid-catalysed. 

The S jS -triphenylphosphorane (316) was obtained when adenosine reacted with triphenylphosphine in the presence of ethyl azodicarboxylate (Scheme 111) 497 Thiobenzoic and benzoic acids cleaved the phosphorus-containing ring to give 5 -substituted adenosines. 

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