Diazo compounds closure

Methylvinyldiazirine (199) rearranges at room temperature in the course of some days. Formation of the linear isomer is followed by electrocyclic ring closure to give 3-methyl-pyrazole. The linear diazo compound could be trapped by its reaction with acids to form esters, while the starting diazirine (199) is inert towards acids (B-71MI50801). 

In the case of sodium 2-(diarylmethylene)cyclopentanone tosylhydrazones 3, however, thermolysis gives the 3//-1,2-benzodiazepines 6 in good yield selected examples are shown. It is suggested that steric constraints in the diazo compounds 4 favor the [1,7] ring closure. The reaction proceeds by way of the intermediates 5, which rearrange to the products by a [1,5] shift of hydrogen.115... 

The toluene- )-8ulfonamido anion may be lost from this, giving the diazo compound directly, or ring closure (which may be reversible) can take place, giving the triazoline anion (2). 

Electrocyclic ring-closure of the diazo compounds (35) and (37) has given the thieno[3,2-cf][l,2]diazepine (36) and the thieno[2,3-i7][l,2]diazepine (38) respectively in very good yields (80JCS(P1)1718>. However, the 3,4-disubstituted thiophene (39) did not give any cyclized product only products ascribable to a carbene intermediate could be isolated. 

The extensive data accumulated by Nakamura and Otsuka, although interpreted by them as being due to the intervention of metal carbene and metallocyclobutane intermediates, can also be rationalized by an alternative mechanism in which coordination of the chiral Co(II) catalyst with the alkene activates the alkene for electrophilic addition to the diazo compound (Scheme 5.4). Subsequent ring closure can be envisioned to occur via a diazonium ion intermediate, without involving at any stage a metal carbene intermediate. 

Phenyl-4,5-diaminoisoxazole hydrochloride (69) reacted with isoamyl nitrite in THF to afford the diazo compound (70), which underwent immediate closure on treatment with aqueous base (5% NaOH) to furnish 3-phenylisoxazolo[4,5-d -1,2,3-triazole (71). The isoxazolotriazole, which resulted in essentially quantitative yield, is a relatively stable compound <70T1393>. Treatment of (71) with acetic anhydride afforded the 6-acetyl derivative, which does not share the stability of its precursor and decomposes rapidly in acid solution (Scheme 15). 

Since it is highly unlikely that the sigmatropic hydrogen shift is reversible, the reaction either proceeds via a reversible first (/ i) step followed by a rate- determining ki step, or via a slow k step followed by a fast k2 step. The correct mechanism has been determined by reacting the diazo compounds deuterated at the ring closure sites in the aryl rings (equation 37). 

Ring closures via benzynes l,2-N,N-Heterocyclics from diazo compounds l,3>Dipolar addition... 

The gold-catalyzed formal cycloaddition reactions of 2-ethynylbenzyl ethers with 8-methylquinoline oxide and ethyl diazoacetate led to a skeletal rearrangement of the benzo[c]furan motif through an attack of the diazo compound on the initial oxonium species in the alkyne activation route, followed by a Roskamp-type rearrangement and ring closure (13AGE7559). 

A review describes the asymmetric epoxidation of allylic alcohols,369 another the role of metal oporphyrins in oxidation reactions.370 jhe TiiOPrMi, catalysed self-epoxidation of allylic peroxides proceeds via an intermolecular mechanism.371 Racemic allyl alcohols can be resolved by asymmetric epoxidation (eq.35).372 a Pd(II)/Mn02/benzoquinone system catalyses the oxidative ring-closure of 1,5-hexadienes (eq.36).373 propenyl phenols are oxidatively degraded to aryl aldehydes and MeCHO in the presence of Co Schiff-base catalysts.374 An Oppenauer-type oxidation with Cp2ZrH2/cyclohexanone converts primary alcohols selectively into aldehydes.375 co macrocycles catalyse the oxidation of aryl liydrazones to diazo compounds in high yields.376 similar Co complexes under CO oxidise primary amines to azo compounds.377 Arene Os complexes in the presence of base convert aldehydes and water slowly into carboxylic acids and H2.378... 

The diazo function in compound 4 can be regarded as a latent carbene. Transition metal catalyzed decomposition of a diazo keto ester, such as 4, could conceivably lead to the formation of an electron-deficient carbene (see intermediate 3) which could then insert into the proximal N-H bond. If successful, this attractive transition metal induced ring closure would accomplish the formation of the targeted carbapenem bicyclic nucleus. Support for this idea came from a model study12 in which the Merck group found that rhodi-um(n) acetate is particularly well suited as a catalyst for the carbe-noid-mediated cyclization of a diazo azetidinone closely related to 4. Indeed, when a solution of intermediate 4 in either benzene or toluene is heated to 80 °C in the presence of a catalytic amount of rhodium(n) acetate (substrate catalyst, ca. 1000 1), the processes... 

In the reaction of 4-diazotriazoles with morpholine, pyrrolidine [83DIS(B)(43)2557], and several other secondary amines (66JMC733), the corresponding triazenes 247 were obtained. Also, in the case of 4-diazo-l,2,3-triazole-5-carboxamide, these compounds could easily be obtained in organic solvents despite the competing intramolecular ring closure to 2,8-diazahypoxanthine. In aqueous media, the intermolecular coupling... 

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