Diazoacetamides compounds

Optical induction emanating from a chiral diazoacetamide is apparently not much higher. The 2-phenylcyclopropanecarboxylates cis-222 and trans-222, obtained in low yield from (N-diazoacetyl)oxazolidones 220,221 and styrene in the presence of Rh2(OAe)4 followed by ethanolysis, showed only small enantiomeric excesses 215). Starting with either diazo compound, the (1/ ) enantiomer was predominant in both cis- and trans-222. 

The dirhodium(n)-catalyzed asymmetric C-H insertion has been recognized as a powerful procedure for the preparation of many interesting compounds.35,43,68,179 Doyle et al. developed an efficient procedure for the enantio-selective syntheses of lactams. - The acyclic terminal diazoacetamides gave moderate enantioselectivity... 

Recently, Yu and co-workers developed an operationally simple catalytic system based on [RuCl2(/>-cymene)]2 for stereoselective cyclization of a-diazoacetamides by intramolecular carbenoid C-H insertion.192 /3-Lactams were produced in excellent yields and >99% m-stereoselectivity (Equation (53)). The Ru-catalyzed reactions can be performed without the need for slow addition of diazo compounds and inert atmosphere. With a-diazoanilide as a substrate, the carbenoid insertion was directed selectively to an aromatic C-H bond leading to y-lactam formation (Equation (54)). 

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... 

Doyle et al.344 and Wee and Liu345 have reported the ring-closing transformation of a-diazoacetamides 108 and 109 to yield 2(3//)-indolinones over Nafion-H [Eq. (5.136)]. In the transformation of compounds 109 the electrophilic intramolecular substitution is followed by decarboxylation.345 Small amounts of 2-azetidinone derivatives (4—10%) formed through a carbene intermediate were also detected. The yield of products from compounds 108 are even higher than observed in the presence of Rh(OAc)2 often applied in the decomposition of diazo compounds.344... 

Having demonstrated the feasibility of their catalytic process, Aggarwal and colleagues explored the use of a chiral sulfide, 12 [77, 78]. It was found that N-SES benzaldimines yielded aziridines 18a-e in excellent enantioselectivity (up to 97% ee), albeit in moderate yield and diastereoselectivity (transicis 3 1—5 1). At catalytic loadings of 12 (20 mol%), Rh2(OAc)4 gave slightly better yields and ee-values than Cu(acac)2 in most cases. The use of alternative diazo compounds such as N,N-diethyl diazoacetamide and ethyl diazoacetate provided moderate enantioselectiv-ities at best, and only stoichiometric sulfide loadings were reported. 

Enantioselective carbenoid cyclopropanation of achiral alkenes can be achieved with a chiral diazocarbonyl compound and/or chiral catalyst. In general, very low levels of asymmetric induction are obtained, when a combination of an achiral copper or rhodium catalyst and a chiral diazoacetic ester (e.g. menthyl or bornyl ester ) or a chiral diazoacetamide ° (see Section 1.2.1.2.4.2.6.3.3., Table 14, entry 3) is applied. A notable exception is provided by the cyclopropanation of styrene with [(3/ )-4,4-dimethyl-2-oxotetrahydro-3-furyl] ( )-2-diazo-4-phenylbut-3-enoate to give 5 with several rhodium(II) carboxylate catalysts, asymmetric induction gave de values of 69-97%. ° Ester residues derived from a-hydroxy esters other than ( —)-(7 )-pantolactone are not as equally well suited as chiral auxiliaries for example, catalysis by the corresponding rhodium(II) (S )-lactate provides (lS, 2S )-5 with a de value of 67%. 

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). 

The iodine in the iodo-compound may be determined in the ordinary manner, or the following simpler method, first used in the investigation of diazoacetamide, may be employed. A weighed quantity of the substance is placed in a tared beaker, dissolved in a little absolute alcohol, and iodine added until a permanent red coloration is obtained. The alcohol is volatilized on the water-bath, the excess of iodine removed by cautious heating, and the crystalline residue weighed. In this case, also, the compound employed must be pure. 

Also A,A-diethyl diazoacetamide and diazoacetate could be used, but higher temperatures were required for the decomposition of the diazo compounds (60°C). 

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