Diazoacetic ester, structure

It was mentioned earlier that catalytic hydrogenation of protoporphyrin-IX (19) produces mesoporphyrin-IX (46), and that this type of vinyl modification has been used in structural degradation methods. The vinyl group can also be modified for degradative purposes by addition of diazoacetic ester, which produces the corresponding cyclopropane derivatives... 

The methods of preparation of i. ost cyclojro-par.e acids involve first the preparation of tAie cyclic ester and subsequent hydrolysis to the free acid. That such hydrolysis did not change tne cyclic structure has been seen to be true ir. all tne cases tnus iar examined i o exceptions to tnis rule will now be studied,ior tney are botn 1,1,2,3 compounds. Aconitic ester and diazoacetic ester give by the usual reactions a cyclopropane ester as follows ... 

Together, DDM, diazoacetic ester, the diazoketones and the diazo-sulphones comprise the most thoroughly investigated of the aliphatic diazocompounds. Direct comparisons between them is limited by the variety of conditions and alkyl structures used in different investigations, but a representative selection of the available data is summarised in Table 3. 

Further observations have been reported on the reactions between diazo compounds and the phosphorus (poly)sulphides (91). The nature of the products depends on the number of sulphur atoms in the polysulphide chain as well as on the nature of R (H or COOEt). Structures (92), (93), and (94) are those of the observed products, the last being peculiar to the reactions involving diazoacetic ester. ... 

Diazo compounds also undergo cycloaddition with fullerenes [for reviews, see (104),(105)]. These reactions are HOMO(dipole)-LUMO(fullerene) controlled. The initial A -pyrazoline 42 can only be isolated from the reaction of diazomethane with [60]fullerene (106) (Scheme 8.12) or higher substituted derivatives of Ceo (107). Loss of N2 from the thermally labile 42 resulted in the formation of the 6,5-open 1,2-methanofullerene (43) (106). On the other hand, photolysis produced a 4 3 mixture of 43 and the 6,6-closed methanofullerene (44) (108). The three isomeric pyrazolines obtained from the reaction of [70]fullerene and diazomethane behaved analogously (109). With all other diazo compounds so far explored, no pyrazoline ring was isolated and instead the methanofullerenes were obtained directly. As a typical example, the reaction of Cgo with ethyl diazoacetate yielded a mixture of two 6,5-open diastereoisomers 45 and 46 as well as the 6,6-closed adduct 47 (110). In contrast to the parent compound 43, the ester-substituted structures 45 and 46, which are formed under kinetic control, could be thermally isomerized into 47. The fomation of multiple CPh2 adducts from the reaction of Ceo and diazodiphenylmethane was also observed (111). The mechanistic pathway that involves the extrusion of N2 from pyrazolino-fused [60]fullerenes has been investigated using theoretical methods (112). 

The reaction is carried out at ambient temperature and nearly complete enantioselectivity (>99%) is observed for mono- and 1,1-disubstituted olefins with diazoacetates. With all copper catalysts, the transkis selectivities in the cyclopropanation of mono-substituted olefins are only moderate. The transkis ratio depends, in this case, mainly on the structure of the diazo ester rather than the chiral ligand (eq 2). It increases with the steric bulk of the ester group of the diazo compound. With the BHT ester, the more stable trans isomer is formed with selectivities up to >10 1. The steric hindrance usually prevents ester hydrolysis, but the BHT group can be removed by reduction with LiAlHj. The trans isomer is even enriched by the reduction procedure because the cis isomer reacts more slowly. 

Enantioselective Intramolecular Carbon-Hydrogen Insertion Reactions. The suitability of Rh2(55-MEPY)4 and Rh2(5R-MEPY)4 for enantioselective intramolecular C-H insertion reactions is evident in results with 2-alkoxyethyl diazoacetates (eq 4). Both lactone enantiomers are available from a single diazo ester. Other examples have also been reported, especially those with highly branched diazo substrate structures. ... 

Pyrethroids occupy a central position among insecticides because of their high selectivity and low toxicity [34]. Chrysanthemic esters (33), the carboxylic acid components of this important class of compounds, can be synthesized by asymmetric cyclopropanation of olefins (cf Section 3.1.7) by diazoacetates in the presence of a chiral Schiff base-Cu complex (Scheme 9 and Structures 34 and 35) [35-37]. 

Enantioselection can be controlled much more effectively with the appropriate chiral copper, rhodium, and cobalt catalyst.The first major breakthrough in this area was achieved by copper complexes with chiral salicylaldimine ligands that were obtained from salicylaldehyde and amino alcohols derived from a-amino acids (Aratani catalysts ). With bulky diazo esters, both the diastereoselectivity (transicis ratio) and the enantioselectivity can be increased. These facts have been used, inter alia, for the diastereo- and enantioselective synthesis of chrysan-themic and permethrinic acids which are components of pyrethroid insecticides (Table 10). 0-Trimethylsilyl enols can also be cyclopropanated enantioselectively with alkyl diazoacetates in the presence of Aratani catalysts. In detailed studies,the influence of various parameters, such as metal ligands in the catalyst, catalyst concentration, solvent, and alkene structure, on the enantioselectivity has been recorded. Enantiomeric excesses of up to 88% were obtained with catalyst 7 (R = Bz = 2-MeOCgH4). 

Intramolecular cyclopropanations with unsaturated diazo ketones have also been reported. Furthermore, enantioselective cyclopropanation with diazomethane can be achieved in up to 75% ee. In detailed mechanistic discussions, a copper(I) species, complexed with only one semicorrin ligand, and formed by reduction and decomplcxation, is suggested as the catalytical-ly active species, cisjtrans Stereoselection and discrimination of enantiotopic alkene faces should take place within a copper-carbene-alkene complex25-54"56. According to these interpretations, cisjtrans selectivity is determined solely by the substituents of the alkene and of the diazo compound (especially the ester group in diazoacetates) and is independent of the chiral ligand structure (salicylaldimine or semicorrin)25. 

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