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- Reactions of azoalkenes derived from hydrazones of ethyl bromopyruvate with electron rich alkenes and heterocyclesPublication . Clarke, S; Gilchrist, Thomas L.; Lemos, A.; Roberts, Tony G.Three hydrazones of ethyl bromopyruvate, the dinitrophenylhydrazone 2a, the toluene-4-sulphonylhydrazone 2b and the t-butoxycarbonylhydrazone 2c, have been reacted with a series of nucleophilic alkenes and heterocycles in the presence of sodium carbonate. Azoalkenes 3 are presumed as intermediates and adducts have been isolated. The azoalkenes derived from hydrazones 2a and 2c are found to be useful electrophiles and electrophilic dienes.
- Azabicyclo[3.2.0]heptan-7-ones (carbapenams) from pyrrolePublication . Gilchrist, Thomas L.; Lemos, A.; Ottaway, Carol J.The azabicyclo[3.2.0]heptan-7-ones 4, 10, 16 and 24 have been prepared from pyrrole. The same general approach has been used for all these derivatives; namely, substitution of pyrrole at the 2- and 5-carbon atoms, catalytic hydrogenation to produce pyrrolidine-2-acetic acid derivatives, and cyclisation using tris(1,3-dihydro-2-oxobenzoxazol-3-yl)phosphine oxide 6. The catalytic hydrogenation of 2,5-disubstituted pyrroles gives only the corresponding cis-2,5-disubstituted pyrrolidines. The hydrogenation proceeds more easily when the nitrogen atom bears a tert-butoxycarbonyl substituent. The N-tert-butoxycarbonylpyrroles 8 and 21 bearing an á-substituent in the acetate side chain were hydrogenated with a high degree of facial stereoselectivity. This allowed the 6-phthalimidoazabicyclo- [3.2.0]heptan-7-one 24 to be isolated as a single diastereoisomer. The X-ray crystal structure of a precursor, the triester, 22a, has been obtained.
- Reaction of pyrroles with ethyl 2-nitroso- and 2-azo-propenoates, and with ethyl cyanoformate N-oxide: a comparison of the reaction pathwaysPublication . Gilchrist, Thomas L.; Lemos, A.The reaction of ethyl 2-nitrosopropenoate 2a with 1 -methylpyrrole, 2.5-dimethylpyrrole and 2.5- diphenylpyrrole has been investigated. In every case the products result from highly regioselective attack at C-2 of the pyrrole by the electrophile. The azopropenoate esters 2b and 2c react similarly with pyrroles, to the extent that even 1 -(triisopropylsilyl)pyrrole is attacked exclusively at the 2-position by the azo ester 2b. In contrast, the nitrile oxide ethyl cyanoformate N-oxide 12 reacts at the 3-position of 2.5- dimethyl- and of 2,5-diphenyl-pyrrole. The reactions of the nitroso and azo esters with pyrroles are interpreted as Diels-Alder cycloadditions with inverse electron demand.