Vinylglycine, reaction with

Vinylglycine was used in the reaction with dibromoformaldoxime for preparation of a biologically active bromoisoxazoline 30, prepared previously from tricholomic acid (79JA1054 80TL229). 

Intermolecular cyclopropanation reactions with ethyl diazoacetate have been employed for the construction of the cyclopropane-containing amino acid 7 (equation 25) Thus, rhodium(II) acetate catalysed decomposition of ethyl diazoacetate in the presence of d-cbz-vinylglycine methyl ester 5 afforded cyclopropyl ester 6 in 85% yield. Removal of the protecting group completed the synthesis of 7. Another example illustrating intermolecular cyclopropanation can be found in Piers and Moss synthesis of ( )-quadrone 8" (equation 26). Intermolecular cyclopropanation of enamide or vinyl ether functions using ethyl diazoacetate has also been used in the synthesis of eburnamonine 9", pentalenolactone E ester 10" and ( )-dicranenone A11" (equations 27-29). 

We have also studied the effect that moving the double bond closer to the amino acid moiety has upon the reactivity of unsaturated a-amino acids [43]. To this end, the cross-metathesis reactions of similarly protected homoallyl-, allyl-and vinylglycine with oct-l-ene were investigated under identical conditions (Eq. 25) (Table 3). 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

Whitney and coworkers [48] reported diastereoselective reactions between chiral nitrones and chiral dipolarophiles. The reaction of Vasella s nitrone 56 with the protected vinylglycine derivative 57 afforded isoxazolidines 58 with high diastereoselectivity (19 1) (Scheme 10.19). After removal of the glycosyl residue, the major isoxazolidine was converted into the antibiotic acivicin [48]. 

In order to determine the stereochemical course at during the normal replacement reaction, Chang and Walsh converted (Z)-DL-[4- H)vinylglycine and ( )-DL-[3,4- H2]vinylglycine to cystathionine in presence of cystathionine y-synthase Salmonella) and cysteine 280). Stereospecific chemical and enzymic degradation of the resultant samples of cystathionine to homoserine followed by comparison of the NMR spectra with those of authentic (4/ )- and (4S)-l-[4- H]homoserine established that cysteine must add to the si face of the vinyl-... 

C. with deuterium and (ii) vinylglycine containing deuterium at only one of the vinyhc positions. Experiments based on this approach were performed [89] and it was shown that in the reaction catalysed by cystathionine-y-synthase, both (4S)-[4- H]-0-succinyl homoserine and (Z)-(4- H]vinylglycine were converted into (45 )-[4- H]cystathionine (Fig. 38). This result is only possible if both transformations proceed through the same intermediate (Fig. 38, 3). These experiments thus show that in the enzymic conversion of (4S)-[4- H]-0-succinyl homoserine (Fig. 38, 1) to products, the terminal double bond of the complex (Fig. 38, 3) has the (Z) configuration. This observation when considered in conjunction with the earlier demonstration that in the conversion the atom is removed [84-86], allows... 

Finally, synthetic samples of (4R)- and (4S)-[4- H,]-0-succinylhomoserine 122, Hg = H, and 122, H = H, respectively, were incubated with the enzyme in the presence of L-cysteine (128, 129), and the H NMR spectra of the resultant samples of cystathione 99a were compared with those of the samples from the vinylglycine incubations. It was evident from these that the /-substitution reaction had occurred with retention of configuration. 

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