2-diazo-l,3-dicarbonyl compounds

Diazomalonic esters, in their behavior towards enol ethers, fit neither into the general reactivity pattern of 2-diazo-l,3-dicarbonyl compounds nor into that of alkyl diazoacetates. With the enol ethers in Scheme 17, no dihydrofurans are obtained as was the case with 2-diazo-l,3-dicarbonyl compounds. Rather, copper-induced cyclo-propanation yielding 70 occurs with ethoxymethylene cyclohexane u4). However,... 

The reaction, formally speaking a [3 + 2] cycloaddition between the aldehyde and a ketocarbene, resembles the dihydrofuran formation from 57 a or similar a-diazoketones and alkenes (see Sect. 2.3.1). For that reaction type, 2-diazo-l,3-dicarbonyl compounds and ethyl diazopyruvate 56 were found to be suited equally well. This similarity pertains also to the reactivity towards carbonyl functions 1,3-dioxole-4-carboxylates are also obtained by copper chelate catalyzed decomposition of 56 in the presence of aliphatic and aromatic aldehydes as well as enolizable ketones 276). No such products were reported for the catalyzed decomposition of ethyl diazoacetate in the presence of the same ketones 271,272). The reasons for the different reactivity of ethoxycarbonylcarbene and a-ketocarbenes (or the respective metal carbenes) have only been speculated upon so far 276). 

Cyclization to a morpholinolactone (59) occurs in the hydrolysis reaction of the di-A-hydroxylethylated compound (60). Compound (59) is rapidly hydrolysed by water to (61) but in file presence of equimolar amounts of amines (RNH2) or ammo acid derivatives (62) forms.56 A novel reaction of cyclic 2-diazo-l,3-dicarbonyl compounds (63) with lactones (64) affords the products (65) in the presence of rhodium acetate, Rh2(OAc)4.57 Lewis acid-promoted intramolecular additions of allylsilanes to lilac tones gave substituted cyclopentanes.58 A proposed transition state guided efforts to improve the stereoselectivity of the reaction. The reaction of a series of /1-lactone derivatives, such as (66)-(68), has been studied and they have been ling cleaved the reaction outcome is both Lewis acid and structure dependent.59... 

Compared to diazonium salts, diazo compounds are generally much less reactive towards nucleophiles than towards electrophiles. As a result of this azo coupling reactions of diazo compounds are the exception rather than the rule. Electron withdrawing substituents on the diazo carbon increase the reactivity towards nucleophiles. Consequently the ability to undergo azo coupling reactions increases from diazomethane to diazocarbonyl- and 2-diazo-l, 3-dicarbonyl compounds. Among the earliest reactions known were those with cyanide and sulfite ions Tertiary phosphines, as opposed to amines, can form stable addition complexes with diazoalkanes probably due to the ability of phosphorus to stabilize the betaine with its empty d orbitals (6). 

Diazo-l,3-dicarbonyl compounds are electrophilic enough to give azo coupling products with reactive aromatic azo coupling components as well as with CH acidic compounds such as P-diketones and p-keto-esters. 

The carbenoid reaction between a-diazo ketones and simple alkenes or styrenes leads to acylcyclopropanes. (For the enantioselective cyclopropanation of styrene with 2-diazo-5,5-dimethylcyclohexane-l,3-dione, see Section 1.2.1.2.4.2.6.3.2.). With ketene acetals, 2,3-dihyd-rofurans are obtained. In contrast, l-acyl-2-oxycyclopropanes or 2-oxy-2,3-dihydrofurans can be formed in reactions with enol ethers and enol acetates the result depends strongly on the substitution pattern of both reaction partners.Whereas simple diazo ketones usually lead to cyclopropanes (Table 15), 3-diazo-2-oxopropanoates and 2-diazo-l,3-dicarbonyl compounds, such as 2-diazoacetoacetates, 3-diazopentane-2,4-dione, and 2-diazo-5,5-dimethylcy-clohexane-1,3-dione, yield 2,3-dihydrofurans and occasionally acyclic structural isomers thereof when reacted with these electron-rich oxy-substituted alkenes. 

Diazo-l,3-dicarbonyl compounds such as alkyl 2-diazo-3-oxobutyTates 57a, b and 3-diazo-2,4-pentanedione 57 c behave like the diazopyruvate 56, as far as their carbenoid cycloaddition behavior is concerned... 

For the investigation of the migratory tendency of groups in Wolff rearrangements, the results obtained with unsymmetrically substituted 2-diazo-l,3-dicarbonyl compounds (8.89) are interesting (8-45). Systematic investigations under comparable thermal and photolytic conditions had already been made at an early time (see review of Meier and Zeller, 1975, Table 2), more recently by Tomioka et al. (1983), by Nikolaev et al. (1991, and earlier references mentioned there), by Nikolaev and Popik (1992), Meier et al. (1988), McMahon et al. (1985), and by others. 

The migration tendency in cyclic 2-diazo-l,3-dicarbonyl compounds was also investigated. The arrows in 8.91, 8.92, and 8.93 indicate the migrating center (after Meier and Zeller, 1975). 

A variety of a-spirolactones and lactams from 2-diazo-l,3-dicarbonyl compounds, (homo)allylic alcohols or amines and acrylic derivatives, in a single synthetic operation by a Wolff rearrangement/a-oxo ketene trapping/cross metathesis/ intramolecular Michael addition sequence has been obtained by Boddaert et al. (2011). 

The nitrosation method is not recommended for a-aminoketones, but it works well for 2-amino-l,3-dicarbonyl compounds, as found by Wolff (1902) for the preparation of 3-diazopentane-2,4-dione (2.31). Cyclic diazo-a, a -diketones, such as 2-diazocyclohexane-l,3-dione (2.32, R=H) and its 5,5-dimethyl derivative (diazo-dimedone, 2.32 R=CH3), can be synthesized without major difficulties (Eistert et al., 1959 Stetter and Kiehs, 1965). The parent compound, diazomalonodialdehyde (2.33) was prepared only in 1973 by Arnold and Sanliova. The smooth formation of diazo-a,a -diketones and the decreased tendency for proton addition at the central C-atom can be explained by the resonance structures 2.31 a-c. 

Arbuzov, B.A., Polozov, A.M., and Polezhaeva, N.A., Catalytic and thermal decomposition of 2-diazo-l,3-diphenyl-l,3-propanedione in dimethyl hydrogen phosphite and O,O-diethyl hydi ogen phospho-rothioite, Zh. Obshch. Khim., 54, 1517, 1984 J. Gen. Chem. USSR (Engl. Transl.), 54, 1351. 1984. Arbuzov, B.A., Polozov, A.M., and Polezhaeva, N.A., P-H addition of carbenoids and carbenes as a method for the synthesis of 2-phospho-substituted 1,3-dicarbonyl compounds, Dokl. Akad. Nauk SSSR, Ser. Khim., 287, 849, 1986 Dokl. Chem. (Engl. Transl.), 287, 69, 1986. 

Bis(diazo)cyclohexane-l,2,4,5-tetraone (5.18) is an interesting borderline case between l,3-dicarbonyl-2-diazocycloalkanes and quinone diazides (5.19, also the 1,2-isomer). We discussed the latter compounds in the book on aromatic diazo com-... 

As indicated earlier in this section, there are still contradictory proposals for the mechanism(s) leading from 2-diazo-l-carbonyl and -1,3-dicarbonyl compounds via Wolff rearrangements to ketenes (Scheme 8-43). Nikolaev and Popik s investigation (1992) demonstrates that compounds that are appearently similar in structure may be characterized by quite different reaction pathways in 8-43. 

The concept of activation of enediyne antibiotics by photolysis of an enediyne chromophore has been developed using a diazo compound. Irradiation of 11-membered enediynes containing an a-diazo-p,p-dicarbonyl fragment leads, via the Wolff rearrangement, to reactive 10-membered structures. Thus, photolysis of 2-diazo-6,7-benzocycloundeca-4,8-diyn-l,3-dione produced the ketoester 3.479 which via enolization undergoes fast cycloaromatization to the reactive diradical 3.480, which in the presence of hydrogen donors produces dihydroanthracene (Scheme 3.17) [245]. 

---