A Conjugate Addition Approach to Diazo‐Containing Scaffolds with β Quaternary Centers

Structurally complex diazo‐containing scaffolds are formed by conjugate addition to vinyl diazonium salts. The electrophile, a little studied α‐diazonium‐α,β‐unsaturated carbonyl compound, is formed at low temperature under mild conditions by treating β‐hydroxy‐α‐diazo carbonyls with Sc(OTf)₃. Conjugate addition occurs selectively at the 3‐position of indole to give α‐diazo‐β‐indole carbonyls, and enoxy silanes react to give 2‐diazo‐1,4‐dicarbonyl products. These reactions result in the formation of tertiary and quaternary centers, and give products that would be otherwise difficult to form. Importantly, the diazo functional group is retained within the molecule for future manipulation. Treating an α‐diazo ester indole addition product with Rh₂(OAc)₄ caused a rearrangement to occur to give a 2‐(1H‐indol‐3‐yl)‐2‐enoate. In the case of diazo ketone compounds, this shift occurred spontaneously on prolonged exposure to the Lewis acidic reaction conditions.     

Lewis acid-mediated reactions of donor-acceptor cyclopropanes with diazo esters

The reactions of diazo esters with 2-arylcyclopropane-1,1-dicarboxylates, the represen- tatives of donor-acceptor cyclopropanes (DACs), mediated by Sc(OTf)₃, SnCl₄, and GaCl₃ proceeded with nitrogen elimination to give the C—C coupling products. No products of the formal [3+3] cycloaddition of diazo compounds to DACs were formed but the main reaction direction was addition of diazo ester to either 1,3- or 1,2-zwitterions generated upon Lewis acid-mediated cyclopropane ring opening giving rise to new 1,4- and 1,3-zwitterionic inter- mediates. The formed intermediates underwent further fragmentations and rearrangements to give substituted cyclopropanedi-, -tri-, and -tetracarboxylates. Mechanistic aspects of the observed reactions were discussed.     

Rhodium(II)‐Catalyzed Inter‐ and Intramolecular Cyclopropanations with Diazo Compounds and Phenyliodonium Ylides: Synthesis and Chiral Analysis

Different classes of cyclopropanes derived from Meldrum's acid (=2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione; 4 ), dimethyl malonate ( 5 ), 2‐diazo‐3‐(silyloxy)but‐3‐enoate 16 , 2‐diazo‐3,3,3‐trifluoropropanoate 18 , diazo(triethylsilyl)acetate 24a , and diazo(dimethylphenylsilyl)acetate 24b were prepared via dirhodium(II)‐catalyzed intermolecular cyclopropanation of a set of olefins 3 (Schemes 1 and 4–6). The reactions proceeded with either diazo‐free phenyliodonium ylides or diazo compounds affording the desired cyclopropane derivatives in either racemic or enantiomer‐enriched forms. The intramolecular cyclopropanation of allyl diazo(triethylsilyl)acetates 28, 30 , and 33 were carried out in the presence of the chiral dirhodium(II) catalyst [Rh₂{(S)‐nttl)₄}] ( 9 ) in toluene to afford the corresponding cyclopropane derivatives 29, 31 and 34 with up to 37% ee (Scheme 7). An efficient enantioselective chiral separation method based on enantioselective GC and HPLC was developed. The method provides information about the chemical yields of the cyclopropane derivatives, enantioselectivity, substrate specifity, and catalytic activity of the chiral catalysts used in the inter‐ and intramolecular cyclopropanation reactions and avoids time‐consuming workup procedures.     

Reactions of diazo esters with electron-deficient alkenes in the presence of Lewis acids

1,3-Dipolar cycloaddition reaction of diazo esters to electron-deficient dipolarophiles to yield the corresponding 1- or 2-pyrazolines was found to be significantly accelerated with Lewis acids (Yb(OTf)₃, Sc(OTf)₃, GaCl₃, EtAlCl₂). The use of GaCl₃ as the catalyst leads to the acceleration not only of the 1,3-dipolar cycloaddition reaction, but also subsequent insertion of the CHCO₂Me electrophilic fragment of methyl diazoacetate into the N-H bond of 2-pyrazolines formed. Such Lewis acids as SnCl₄, BF₃, TiCl₄, and In(OTf)₃ are not efficient in the described processes, since they rapidly decompose starting diazo compounds.     

Unique chemoselective Mukaiyama aldol reaction of silyl enol diazoacetate with aldehydes and acetals catalyzed by MgI2 etherate

Functionalized diazo acetoacetates are prepared by an efficient Mukaiyama aldol reaction between 3-TBSO-2-diazo-3-butenoate with aldehydes and acetals under mild reaction conditions. A variety of substituted aldehydes and the corresponding acetals are both accessible in good to excellent yields through this methodology. MgI₂ etherate (MgI₂·(OEt₂)_n) is the preferred catalyst and, the addition proceeds without decomposition of the diazo moiety. In addition, this MgI₂·(OEt₂)_n-catalyzed Mukaiyama aldol reaction shows unique chemoselectivity towards aldehydes and acetals.     

Covalent binding of fullerene C<Subscript>60</Subscript> to pharmacologically important compounds

The cycloaddition of diazo compounds derived from α-tocopherol, betulinic acid, ursolic acid, and Trolox methyl esters to fullerene C₆₀ in the presence of a Pd(acac)₂-PPh₃-Et₃Al catalytic system was performed. The reactions of the diazo compounds derived from the above-mentioned pharmacologically important compounds with fullerene C₆₀ in the presence of the Pd(acac)₂-PPh₃-Et₃Al system (1: 2: 4) afford predominantly the previously inaccessible pyrazolinofullerenes. A change in the component ratio of the Pd(acac)₂-PPh₃-Et₃Al catalyst from 1: 2: 4 to 1: 4: 4 favors the formation of methanofullerenes exclusively.     

Cyclopentanes from N‐Aminoglyconolactams: Reaction Mechanism and Improved Access to Diazocyclopentanones

One of the two mechanisms to rationalize the Pb(OAc)₄ oxidation of 1 to 2 and 3 postulates the intermediate generation of a carbene 25 via the acetoxy‐diazepinone 22 and the oxadiazoline 23 (Scheme 2). This mechanism was excluded on the basis of the oxidation of the diazepinone 32 that was synthesized in six steps from the ribonolactone 26 . Oxidation of 32 with Pb(OAc)₄ provided the unstable acetoxy‐diazepinone intermediate 22 , its C(5) epimer, and the stable 5‐O‐acetyl‐1,5‐ribonolactone 33 ; the ¹H‐NMR spectra of the products of the oxidation of 32 and the decomposition of 22 showed no evidence for the formation of the acetoxy epoxide 2 and the diazo ketone 3 , excluding 22 as intermediate in the oxidation of 1 . To increase the yield of the diazo‐cyclopentanones, we oxidized the acetohydrazide 34 , the 4‐toluenesulfonohydrazide 44 , and the N,O‐diacetate 46 with Pb(OAc)₄. Oxidation of the acetohydrazide 34 with Pb(OAc)₄ led to a higher yield of the diazo ketone 3 (40%) than oxidation of the N‐amino‐ribonolactam 1 without affecting the yield of 2 . Oxidation of the 4‐toluenesulfonohydrazide 44 gave mostly the product 45 of C‐acetoxylation, while the analogous oxidation of 46 gave the acetoxy lactone 33 ; neither 2 nor 3 could be detected among the products, excluding 46 as intermediate of the oxidation of 34 . Oxidation of the N‐acetamido‐lyxonolactam 47 with Pb(OAc)₄ provided the diazo ketone 8 (77 vs. 37% from 5 ); higher yields of diazo ketones resulted also from the oxidation of the acetohydrazides 48 and 49 .     

π-Coordination de doubles liaisons azoteazote et carboneazote sur les fragments Cp2NbH et Cp2TaH

The trihydrides Cp₂MH₃ (M = Nb, Ta) react with diphenyl diazomethane giving Cp₂M(diazo)H complexes in which the diazo molecule is η²-N,N-bonded to the metal. When Cp₂TaH₃ is treated with the isonitrile CNCMe₂CH₂C(Me)₃, the complex Cp₂Ta[CH(CN)NR]H (R = CMe₂CH₂CMe₃) is obtained which contains an η²-coordinated CN bond.     

Collision-induced dissociation study of cyclization of α-diazo-ω-arylsulphonylaminoalkan-2-ones

The collision-induced dissociation mass-analysed ion kinetic energy (CID MIKE) spectra (electron impact and chemical ionization) of five α-diazo-ω-arylsulphonylaminoalkan-2-ones and corresponding N-arylsulphonylazetidin-3-ones and N-arylsulphonylpyrrolidin-3-ones were studied. The [M ? N₂]⁺˙ and [MH ? N₂]⁺ ions of two types of the diazo ketones provide CID MIKE spectra similar to those of the corresponding M⁺˙ and MH⁺ of the heterocyclic compounds, i.e. a cyclization analogous to that in solution takes place. For the other three types of diazo compounds the Wolff rearrangement prevails in both the gas and liquid phases. The effect of the substituents on the cyclization process was studied. The data obtained permit the results of acid-catalysed cyclization of similar diazo ketones to be predicted on the basis of their CID MIKE spectra. Chemical ionization provides a closer similarity with reactions in solution than electron impact ionization, which can be rationalized by the protonation of the diazo ketone molecule being the driving force of the cyclization reaction either in solution or in the ion source of a mass spectrometer.     

Reaction of Aliphatic Diazo Compounds with Dinitrogen Trioxide. A Facile route to 3,4-Disubstituted 1,2,5-Oxadiazole-2-oxides(Furoxans)

As part of our continuing studies¹of the chemistry of diazo compounds, we have investigated the reaction of α-diazosulfones, α-diazoketones and ethyl diazoacetate with dinitrogen trioxide. When a solution of the diazo compound is allowed to react at 0–5° with excess n₂O₃ ² in CH₂Cl₂, and almost instantaneous evolution of a gas (presumably nitrogen) is observed. Work-up afforded 3,4–disubstituted furoxans (I–VII, see Table) in good Yields.     

重氮化合物与醇的插入反应合成α-烷氧基-β-二羰基化合物

研究了在过渡金属配合物催化下α-重氮-β-二羰基化合物与醇的插入反应, 考察了重氮化合物的结构、醇的结构、催化剂的性质、反应溶剂和反应温度对这一反应的影响. 发现当重氮化合物与甲醇的物质的量比为1∶10, 1 mmol% Rh₂(OAc)₄为催化剂和回流的苯的条件下, 反应能够以高的化学产率生成α-甲氧基-β-二羰基化合物. 手性醇衍生的重氮乙酰乙酸酯反应的产物中两种非对应异构体的比例为3∶2～1∶1.     

Ruthenium(II)‐Catalyzed C−H Activation of Imidamides and Divergent Couplings with Diazo Compounds: Substrate‐Controlled Synthesis of Indoles and 3H‐Indoles

Indoles are an important structural motif that is commonly found in biologically active molecules. In this work, conditions for divergent couplings between imidamides and acceptor–acceptor diazo compounds were developed that afforded NH indoles and 3H‐indoles under ruthenium catalysis. The coupling of α‐diazoketoesters afforded NH indoles by cleavage of the C(N₂)?C(acyl) bond whereas α‐diazomalonates gave 3H‐indoles by C?N bond cleavage. This reaction constitutes the first intermolecular coupling of diazo substrates with arenes by ruthenium‐catalyzed C?H activation.     

Synthesis of functionally substituted methanofullerenes and study of their tribological properties

Possibility of synthesizing functionally substituted methanofullerenes by cycloaddition of diazo derivatives of methionine and threonine to C₆₀ fullerene in the presence of a three-component catalytic system Pd(acac)₂-PPh₃-Et₃Al was examined. Tribological characteristics of the resulting compound as an additive to an industrial oil were studied.     

New Syntheses of Diazo Compounds

Diazo compounds (R¹R²C?N₂) are known as versatile and useful substrates for an array of chemical transformations and, therefore, diazo chemistry is still far from losing anything of its long‐standing fascination. In addition to many studies on the subsequent chemistry of the diazo group, the inventory of methods for the preparation of diazo compounds is continuously supplemented by new methods and novel variations of established procedures. Several of these synthetic approaches take into account the lability and remarkable chemical reactivity of certain classes of diazo compounds, and environmentally more benign procedures also continue to be developed.     

Pd–Carbene Migratory Insertion: Application to the Synthesis of Trifluoromethylated Alkenes and Dienes

Pd‐catalyzed cross‐coupling of halides with CF₃‐substituted diazo compounds or N‐tosylhydrazones has been explored for the synthesis of CF₃‐substituted alkenes and 1,3‐butadienes. Pd–carbene migratory insertion plays the key role in these transformations.     

Synthesis of 3-keto-4-diazo-5-α-dihydrosteroids as potential irreversible inhibitors of steroid 5-α-reductase

3-Keto-4-diazo-5-α-dihydrosteroids are prepared using the Hendrickson diazo transfer reaction on the corresponding β-diketones, which are available from 3-ketoΔ-4-steroids $\text{via}$ Li/NH₃ reduction and acylation of the kinetic enolate.     

Rhodium(II)‐Catalyzed Inter‐ and Intramolecular Enantioselective Cyclopropanations with Alkyl‐Diazo(triorganylsilyl)acetates

The intermolecular cyclopropanation of styrene with ethyl diazo(triethylsilyl)acetate ( 1a ) proceeds at room temperature in the presence of chiral Rh^II carboxylate catalysts derived from imide‐protected amino acids and affords mixtures of trans‐ and cis‐cyclopropane derivatives 2a in up to 72% yield but with modest enantioselectivities (<54%) (Scheme 1 and Table 1). Protiodesilylation of a diastereoisomer mixture 2a with Bu₄NF is accompanied by epimerization at C(1) (→ 3 ). The intramolecular cyclopropanation of allyl diazo(triethylsilyl)acetate ( 8a ), in turn, affords optically active 3‐oxabicyclo[3.1.0]hexan‐2‐one ( 9a ) with yields of up to 85% and 56% ee (Scheme 3 and Table 2). Similarly, the (2Z)‐pent‐2‐enyl derivative 8d reacts to 9d in up to 77% yield and 38% ee (Scheme 3 and Table 3). In contrast, the diazo decomposition of (2E)‐3‐phenylprop‐2‐enyl and 2‐methylprop‐2‐en‐1‐yl diazo(triethyl‐silyl)acetates ( 8b and 8c , resp.) is unsatisfactory and gives very poor yields of substituted 3‐oxabicyclo[3.1.0]hexan‐2‐ones 9b and 9c , respectively (Table 3).     

Reactivity of Carbenes and Related Compounds towards Molecular Nitrogen

The thermal N₂ exchange of a number of ¹⁵N-labelled diazo compounds was studied in solution. The compounds involved were 3-diazo-1-methylindolin-2-one ( 1 ), 9-diazofluorene ( 2 ), 5-diazo-1,3-cyclopentadiene-1,2,3,4-tetracarbonitrile ( 3 ), 2-diazo-2H-imidazole-4,5-dicarbonitrile ( 4 ), 4-diazocyclohexa-2,5-dienone ( 5 ), and the conjugate acids of 4 and 5 , namely 4,5-dicyano-1H-imidazole-2-diazonium ion ( 6 ) and 4-hydroxybenzenediazonium ion ( 7 ). Only 1 , 4 , 6 , and 7 exchange their diazo group with ‘external’ molecular N₂. The results are explained on the hypothesis that only organic species which have an empty σ orbital and which are effective in π electron back-donation are able to react with N₂. Thus, reaction with carbenes is likely to occur only if the carbene is in the ¹A₂ singlet state and if its electrophilicity is high.     

Allgemeine Basenkatalyse der Azokupplung von o-Diazophenolen. 19. Mitteilung zur Kenntnis der Azokupplungsreaktion

1. The kinetics and the mechanism of the diazo coupling reaction of 2-diazophenol-4-sulphonic acid with 1-naphthol-2-sulphonic acid have been investigated at 0° and ionic strength I=0.45. 2. The pK_a-value of the hydroxyl group in 2-diazophenol-4-sulphonic acid has been determined: pK_a=- 0.04 ± 0.10. It is the diazonium-phenolate anion which actually enters into the diazo coupling reaction. 3. The reaction is subject to general base catalysis. It is shown that no intermediate is enriched during the reaction at pH 11.3–11.6 which proceeds by a two-step mechanism with a steady state intermediate.     

Organoaluminum‐mediated polymerization of diazoketones

Polymerization of diazoketones mediated by organoaluminum compounds was investigated. Trialkylaluminum R₃Al (R = iBu, Et, Me) and diisobutylaluminum hydride (DIBAL) polymerized (E)‐1‐diazo‐3‐nonen‐2‐one ( 1 ) to give polymers with M_n = 2000–3500, which contained nearly 33 mol % of azo group (? N?N? ) along with the dominant acylmethylene unit in the main chain. On the other hand, when (E)‐1‐diazo‐4‐phenyl‐3‐buten‐2‐one ( 2 ) was used as a monomer for the organoaluminum‐mediated polymerization, the resulting polymers had ethylidene (? CH[CH₃]? ) units in the main chain along with acylmethylene and azo group, as a result of reductive cleavage of the acyl group during the polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5209–5214, 2007