Diazo alkanes 3 + 2 cycloaddition reactions

Trifluoromethyl-substituted diazonium betaines [176]. Synthetic routes to trifluoromethyl-substituted diazo alkanes, such as 2,2,2-trifluorodiazoethane [ 177, 7 78, 179] and alkyl 3,3,3-trifluoro-2-diazopropionates [24], have been developed Rhodium-catalyzed decomposition of 3,3,3-tnfluoro-2-diazopropionates offers a simple preparative route to highly reactive carbene complexes, which have an enormous synthetic potential [24] [3-1-2] Cycloaddition reactions were observed on reaction with nitnles to give 5-alkoxy-4-tnfluoromethyloxazoles [750] (equation 41)... 

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... 

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... 

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. 

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