Diazo alkanes formation

A neutral diazo compound can be considered as both a nucleophile and an electrophile. Thus, it can be substituted by the combination of an electrophilic moiety and a nucleophilic moiety (X+ Nu ") (Scheme 8). In practice, the diazomethyl group is transformed to the fluoromethyl group by treatment with hydrogen fluoride/pyridine mixture (70 30 w/w) (X = H Nu = F), or to the halofluoromethyl group by addition of A-halosuccinimide in the same medium (X = Cl, Br, I Nu = F), e.g. formation of l.16 The reaction can be performed on secondary diazo alkanes, diazo ketones or diazo esters.16 90 316... 

Furthermore, a novel electrophilic sp2 C-H bond activation and its application for the preparation of a-diazomethylzirconium complexes were also recently reported. Treatment of complexes 53 with ethyldiazoacetate or with trimethylsilyldiazo methane affords the C-a-metallated diazo alkane complexes 63-66 (Scheme 15). When 53a,b were allowed to react with the non terminal diazo derivative 67, the pyrazoles 70 and 71 were obtained in good yield. Formation of the pyrazoles could be rationalized by O-H bond activation of the enol tautomer of 67, leading to the zirconocene diazo intermediates 68 and 69 which... 

The C-a-metallated diazo alkane complex 63 when reacted with phenyliso-cyanate is transformed into the 1,2,3-triazolato zirconocene enolate complex 74. An identical reaction conducted with naphthyl isocyanate gave the triazole 75. It is reasonable to propose for the formation of 74 and 75, as a first step of the reaction, a [3 + 2] dipolar cycloaddition of the diazo function with the isocyanate group, with transient formation of 72 and 73 (Scheme 16). Then, due to the high... 

Diazo alkanes are sometimes involved as intermediates in deamination, especially in aprotic solvents . The counterion and micellar formation are other factors which can determine the products of deamination. 

Together with the addition of C-nucleophiles, cycloadditions represent the most important reaction for the formation of C-C-bonds with the fullerene framework [28, 29, 110]. [3+ 2]Cycloaddition of diazo alkanes to 6-6 bonds was... 

Alkylation describes the reaction where an active hydrogen is replaced with an alkyl group, for example, a methyl group. Most polar groups can be alkylated, and many reagents can be used, for example, alkyl halogenides, diazo alkanes, and N,N -dimethylformamide dialkyl acetal. An example of an alkylation is the formation of methyl esters of fatty acids by using methanolic BF3, where boron trifluoride (BF3) acts as a catalyst. 

Oxa-l -silabicyclo[ . 1,0 alkanes (n = 3 111 n = 4 113) were the only products isolated from the photochemical, thermal or transition-metal catalyzed decomposition of (alkenyloxysilyl)diazoacetates 110 and 112, respectively (equation 28)62. The results indicate that intramolecular cyclopropanation is possible via both a carbene and a carbenoid pathway. The efficiency of this transformation depends on the particular system and on the mode of decomposition, but the copper triflate catalyzed reaction is always more efficient than the photochemical route. For the thermally induced cyclopropanation 112 —> 113, a two-step noncarbene pathway at the high reaction temperature appears as an alternative, namely intramolecular cycloaddition of the diazo dipole to the olefinic bond followed by extrusion of N2 from the pyrazoline intermediate. A direct hint to this reaction mode is the formation of 3-methoxycarbonyl-4-methyl-l-oxa-2-sila-3-cyclopentenes instead of cyclopropanes 111 in the thermolysis of 110. 

Monohalo or dihalo alkanes, carboxylic acids, or ketones are obtained on treating diazoalkanes,1167 diazocarboxylic esters,1168 or diazo ketones with hydrogen halides or halogens. The reaction usually occurs at room temperature or below. However, preparative importance attaches only to the formation of the halo ketones from diazo ketones they are obtained free from isomers (cf. page 189). 

Many rhodium(II) complexes are excellent catalysts for metal-carbenoid-mediated enantioselective C-H insertion reactions [101]. In 2002, computational studies by Nakamura and co-workers suggested the dirhodium tetracarboxylate catalyzed diazo compounds insertion reaction to alkanes C-H bonds proceed through a three-centered hydride-transfer-like transition state (Fig. 25) [102]. Only one rhodium atom of the catalyst is involved in the formation of rhodium carbene intermediate, while the other rhodium atom served as a mobile ligand, which enhanced the electrophilicity of the first one and facilitate the cleavage of rhodium-carbon bond. In this case, the metal-metal bond constitutes a special example of Lewis acid activation of Lewis acidic transition-metal catalyst. 

---