Diazoacetamides metallations

With respect to the large number of unsaturated diazo and diazocarbonyl compounds that have recently been used for intramolecular transition metal catalyzed cyclopropanation reactions (6-8), it is remarkable that 1,3-dipolar cycloadditions with retention of the azo moiety have only been occasionally observed. This finding is probably due to the fact that these [3+2]-cycloaddition reactions require thermal activation while the catalytic reactions are carried out at ambient temperature. A7-AUyl carboxamides appear to be rather amenable to intramolecular cycloaddition. Compounds 254—256 (Scheme 8.61) cyclize intra-molecularly even at room temperature. The faster reaction of 254c (310) and diethoxyphosphoryl-substituted diazoamides 255 (311) as compared with diazoacetamides 254a (312) (xy2 25 h at 22 °C) and 254b (310), points to a LUMO (dipole) — HOMO(dipolarophile) controlled process. The A -pyrazolines expected... 

A complication in aziridination is that metal carbenoids can react directly with some imines to yield aziridines. Fortunately, imines bearing electron-withdrawing groups are less reactive to carbenoids and more reactive to ylides than electron-rich imines. Thus, N-tosyl, N-diphenylphosphinyl and N-[-(tri-methylsilyl)ethansulfonyl] imines (-(trimethylsilyl)ethansulfonyl = SES) were all suitable substrates using dimethylsulfide and Rh2(OAc)4, with no background reaction detected [77, 78]. Phenyldiazomethane, N,N-diethyl diazoacetamide and ethyl diazoacetate could be used as the diazo component, although the latter two required temperatures of 60 °C to decompose. 

Enantiocontrol in intramolecular cyclopropanation reactions of diazoacetamides has been developed to levels comparable with those now accessible with diazoesters. Several substituent variations in Eq. (20) are summarized in Table 3, which reveals examples where ee s exceed 90%. In general diazoamides have a conformational feature which differs from their diazoester counterparts, namely, the relatively slow syn-anti isomerization by rotation about the N-CO bond. If the interconversion of (18) and (19) or their respective metal carbenes is slow relative to the reaction timescale [50], only isomer (18) can lead to intramolecular cyclopropanation. However, an alternative process to which (18) is prone un-... 

Metal-catalyzed decomposition of a-diazocarbonyls followed by intramolecular carbenoid C-H insertion is an effective means to access important heterocyclic compounds [36, 221-223]. A variety of p- and y-lactams have been synthesized from a-diazoacetamides. Several dirhodium catalysts are used for this transformation [224—228]. Diruthenium catalysts with acetate (1), pyridonate (60), sacchari-nate (63), and triazenide (69) bridges were employed as potential catalysts for this reaction. A new class of compounds containing calix [4]arenedicarboxylate moiety (70-72) were also used (Scheme 42) [67]. The catalytic activity of all these diruthenium(I,I) complexes are compared with dirhodium(II,II) complexes 37 and 73 (Scheme 43). 

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