Diazo-imines

More recently, Williams has described the one pot synthesis of 2-substituted oxazoles 11 by the thermolysis of triazole amides 9 the reaction does not proceed photo-chemically.<92TL1033> Although the reaction does not involve addition to a nitrile, it is an interesting application of a diazo compound since the proposed zwitterionic intermediate 10 is a resonance form of a diazo imine, so formally the reaction may be thought of as a thermal decomposition of a diazo imine (Scheme 6). 

It is known that 1//-1,2,3-triazoles can exist in equilibrium with diazo-imines. In the conversion of 1 into 2 as intermediate the diazo-imine 3 can... 

Ring-chain equilibria of 1,2,3-triazoles and benzotriazoles with the isomeric a-diazo imines result in the well-known Dimroth rearrangement (see Section 4.01.4.1.1). 

Triazoles also serve as a precursor of metal carbene complexes. For instance, Murakami and Fokin independently reported a denitrogenative rearrangement reaction of triazolyl alcohol 69 (Scheme 7.27) [41]. The ring-chain tautomeriza-tion of 69 generates its diazo imine form, which reacts with Rh2(Oct)4 to produce a rhodium carbene complex. The following 1,2-alkyl migration and elimination of rhodium produce enaminone 70. 

The first /3 -lactam was produced by addition of a ketene to an imine and there are now many examples of this type of approach. The ketenes are most frequently generated in situ from acid chlorides by dehydrohalogenation, but have also been produced from diazo ketones, by heating of alkoxyacetylenes and in the case of certain cyanoketenes by thermolysis of the cyclic precursors (162) and (163). 

The addition of diazo compounds generally leads to three membered tings, although in special cases, linear adducts with an intact diazo group [110] or l,3,4-oxadiazol-3-ines [111] can be isolated Most diazo compounds are unstable and yield oxirans and aziridines [112,113,114] Aziridines are obtained exclusively on reaction of certain polyfluorinated acyl imines with diazomethane [115]... 

Halogenated and halogenoalkyl substituted imines react with diazo alkanes under very mild conditions and preferentially yield aziridines [5, 146 147] Diazonium betaines have been considered as intermediates of these reactions [148,... 

Of course, the key limitation of the ylide-mediated methods discussed so far is the use of stoichiometric amounts of the chiral reagent. Building on their success with catalytic asymmetric ylide-mediated epoxidation (see Section 1.2.1.2), Aggarwal and co-workers have reported an aza version that provides a highly efficient catalytic asymmetric synthesis of trans-aziridines from imines and diazo compounds or the corresponding tosylhydrazone salts (Scheme 1.43) [68-70]. 

Reactions between imines and a-diazo carboxylates afford aziridine-2-carboxylates [55]. An asymmetric version of this reaction using chiral nonracemic catalysts has been described [53, 56-58]. As an example, catalytic aziridination of inline 44 (Scheme 3.14) with ethyl diazoacetate in the presence of 10% catalyst generated... 

These complexes can be isolated in some cases in others they are generated in situ from appropriate precursors, of which diazo compounds are among the most important. These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, palladium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Ethyl a-diazoacetate reacts with styrene in the presence of bis(ferrocenyl) bis(imine), for example, to give ethyl 2-phenylcyclopropane-l-carboxylate. Optically active complexes have... 

Alkylation and hydrolysis of imines alkylation of aldehydes 10-107 Alkylation and hydrolysis of dithianes 10-108 Alkylation and hydrolysis of oxazines and similar compounds 10-109 Reaction of diazo aldehydes with boranes... 

Aziridines have been synthesized, albeit in low yield, by copper-catalyzed decomposition of ethyl diazoacetate in the presence of an inline 260). It seems that such a carbenoid cyclopropanation reaction has not been realized with other diazo compounds. The recently described preparation of 1,2,3-trisubstituted aziridines by reaction of phenyldiazomethane with N-alkyl aldimines or ketimines in the presence of zinc iodide 261 > most certainly does not proceed through carbenoid intermediates rather, the metal salt serves to activate the imine to nucleophilic attack from the diazo carbon. Replacement of Znl2 by one of the traditional copper catalysts resulted in formation of imidazoline derivatives via an intermediate azomethine ylide261). 

The outcome of the copper-catalyzed decomposition of a diazo compound in the presence of a 1,1-diarylmethanimine depends on the nature of the diazo compound. With diazodiphenylmethane, the N/H insertion product 281 and the isomeric imine... 

Although formally the product of 1,4-addition of the carbene to the ADC 4n unit, 1,3,4-oxadiazolines probably arise via initial nucleophilic attack of the diazo compound to give, after loss of N2, a dipolar intermediate. This intermediate azomethine imine can collapse directly to give the oxadiazoline,... 

In 2007, Maruoka et al. introduced chiral dicarboxylic acids consisting of two carboxylic acid functionalities and an axially chiral binaphthyl moiety. They applied this new class of chiral Brpnsted acid catalyst to the asymmetric alkylation of diazo compounds withA-Boc imines [91]. The preparation of the dicarboxylic acid catalysts bearing aryl groups at the 3,3 -positions of the binaphthyl scaffold follows a synthetic route, which has been developed earlier in the Maruoka laboratory [92]. 

Scheme 73 Fiiedel-Crafts-type alkylation of diazo compounds with A-Boc imines...

The vapor-phase pyrolysis of 4-hydroxy-1,2,3-triazole and its iV-methyl derivative affords methan-imine and its A-methyl analog. Analysis of the reaction path by the MNDO method shows the presence of two stable or metastable isomers, (liif)-4-hydroxy-l,2,3-triazole and its ketone protomer <89NJC551>. 4-Diazo-1,2,3-triazoles (122) thermolyze or photolyze in benzene to 4//-l,2,3-tri-azolylidenes (123) which convert benzene to 4-phenyl-1,2,3-triazoles and/or isomerize to a-diazo-nitriles (124). Intermediates (124) react with benzene via a carbene to give addition, ring expansion or substitution products (Scheme 17) <82TL5115>. The similar thermolysis of diazotriazoles in substituted benzene gives complex mixtures in which all of the components are sometimes impossible to isolate and identify <90AHC(48)65>. 

The [3 + 2] cycloaddition of diazo compounds to imines or nitriles is an alternative approach to the preparation of 1,2,3-triazoles and 1,2,3-triazolines. For reviews, see CHEC-I <84CHEC-I(5)7I7>. 

The benzoylphenylketene generated from 321 displayed a pronounced tendency to form chemospecific [2+4] Diels-Alder adducts with the C=N group of keto-imines. When compounds 328, derived from />-aminoacetophe-none and aromatic aldehydes, were reacted with a-diazo-/3-diketone 321, 2,3-dihydro-4//-l,3-oxazin-4-ones 329 were obtained via the addition of benzoylphenylketene to the C=N bond, and no formation of the corresponding C=0 adducts, 477-l,3-dioxin-4-ones, was observed (Equation 31) <2001J(P1)2266>. 

The cycloaddition reactions of the unsymmetrical a-diazo-/3-diketone, 2-diazo-l-phenyl-l,3-butanedione 330, with diaryl imines 331 took place with high regioselectivity, affording exclusively the 6-methyl-5-phenyl-substituted 477-l,3-oxazin-4-ones 332 via the acetylphenylketene, generated by the thermal Wolff rearrangement of 330 (Equation 32) <2002HAC165>. 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

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