Arthur J. Birch

Studies in relation to biosynthesis—XLII: The structural elucidation and some aspects of the biosynthesis of the brevianamides-A and -E

Abstract Five related metabolites have been isolated from the mould, Penicillium brevi-compactum Dierckx. The structural elucidation and biosynthesis of two of these, brevianamides-A and -E, is discussed. They are shown to be biogenetically derived from tryptophan, proline and mevalonic acid. The UV chromophores of four of these compounds are related to the 2,2-disubstituted Ψ-indoxyl system. Brevianamide-A probably has the structure 8, and brevianamide-E is probably 25.

Studies in relation to biosynthesis—XLIV : Structural elucidations of brevianamides-B, -C, -D and -F

Abstract The culture medium of Penicillium brevi-compactum Dierckx contains the neutral metabolites, brevianamides-A to -F. The structures of-A and -E 1 , based upon spectroscopic, biogenetic and degradative evidence, have been reported. 2 Preparative TLC of the residues from the crystallization of brevianamide-A yields -B, -C and -D in the pure state. High resolution mass-spectrometry shows them to have the formula C 21 H 23 N 3 O 3 , isomeric with brevianamide-A. Brevianamide-B is shown by inter-conversion with brevianamide-A to be a stereoisomer. Brevianamides-C and -D are shown to contain a 2′-indoxylidenealkane chromophore and are the stereoisomers ( 1 ) and ( 2 ) respectively. For spectral comparisons the cis and trans isomers of 2,2-dimethyl-1-(2′-indoxyliden)propane have been synthesized. Brevianamides-C and -D are obtained by irradiation with visible light of brevianamide-A.

The structure and some aspects of the biosynthesis of pleuromutilin

Abstract Evidence is presened which confirms the structure I for pleuromutilin. The specific incorporation of [ 14 C] acetic and mevalonic acids verifies its diterpenoid nature, and some aspects of its stereochemistry are discussed.

STEREOSPECIFIC AND REGIOSPECIFIC FORMATIONS AND REACTIVITIES OF SOME SUBSTITUTED TRICARBONYLCYCLOHEXADIENEIRON COMPLEXES

I,3-Diene-Fe(CO)3 complexes have many synthetic applications for the organic chemist. The Fe(C0)3 can act as a protecting group; it alters reactivities both to electrophilic and, indirectly through derived cations, to nucleophilic processes; it stabilizes otherwise unstable structures, such as cyclohexadienones, and makes them available as the basis of reagents. Above all, it distinguishes between one side of a molecule and the other, often permitting totally stereospecific reactions, including the transfer of asymmetry to new chiral centers by the use of chiral complexes of nonchiral dienes. The discussion here is limited chiefly to our own work on cyclohexadienes. To use such complexes requires the definition of methods for their preparation in good yields in states of purity, both structural and steric. Problems in this area tend, so far, to limit synthetic uses to sequences in which the complex is formed at an early stage, from readily available material. Another difficulty is that many reactions that proceed readily with molecules containing simple substitution patterns, do not d o so with the more complex substituents needed by the organic chemist. Careful consideration must still be given t o alternative methods of formation of desired types of substitution in such complexes.

Asymmetric synthesis of optically active tricarbonyliron complexes of 1,3-dienes

Abstract Asymmetric coordination of prochiral 1,3-dienes to form optically active (diene)Fe(CO)3 complexes has been achieved by direct transfer of the Fe(CO)3 group from chiral enone complexes.

Alkylation of tricarbonylcyclohexadienyliron salts (1) with lithium alkyls

Abstract The salts 1 (Y=H, OMe, Me) react with RLi(R=Me, n-Bu, i-Pr, t-Bu) in CH 2 Cl 2 at low temperature to give 2 and 3 in excellent yields. Nucleophilic addition at the 1-position of 1 (Y=OMe) has been observed for the first time.

Optical resolution of tricarbonyl(1-carboxycyclohexa-1,3-diene) iron and the absolute configuration of the products

Resolution of the acid (1) (shown as the (+)-isomer) into its optically pure (+) and (−) isomers and reduction of the CO2H yields the 2-Me derivative (2) (shown as the (−)-isomer). The absolute configuration of (2) is defined by conversion of the salt (3) of known configuration into (2) and (4). This is the first resolution leading to preparation of pure complexes of known absolute configuration.

Optically active tricarbonyl(cyclohexadienyl)iron(1+) salts: Synthetic equivalents to spatially directed organic cations

Abstract Optically active tricarbonyl (cyclohexdienyl)iron(1+) salts I, II and III are examples of olefin complexes with moleoular asymmetry due to coordination uith a transition metal. Their reactions serve to direct the eventual specific formation of a new chiral centre of known absolute configuration. The absolute configuration of the 2-methoxy-5-methyl salt I is defined its application to the asymmetric synthesis of λ-disubstituted cyclohexenones is described.

Regioselectivity of nucleophilic additions to tricarbonyl[η5-2-methyl-2,4-cyclohexadien-1-yl]iron(1+)PF6-: temperature dependence of hydride reductions

Abstract Reduction of [(η5-CH3C6H6)Fe(CO)3]+PF6− by NaBH4, LiBH4, LiEt3BH and KBu53BH becomes less regioselective at lower temperatures. Regioselectivity of reduction by 9-BBN, however, improves as the temperature is lowered. Factors affecting nucleophilic addition are discussed in terms of likely transition states for the competing processes.

Tricarbonylcyclohexadienyliron complexes : synthetic equivalents of aryl cations; a facile synthesis of 2-aryl-cyclopentenones and its application towards prostaglandin analogues

Abstract Tricarbonylcyclohexadienyliron cations of type 1 are converted, by alkylation with 1,2-bis(trimethylsiloxy)-1-cyclopentene, dehydration and subsequent dehydrogenation, into specifically substituted 2-aryl-2-cyclopentenones.