Pieter S. van Heerden

ENANTIOSELECTIVE SYNTHESIS OF THE FOUR CATECHIN DIASTEREOMER DERIVATIVES

Abstract Asymmetric dihidroxylation of (E)-1-(3,4-dimethoxyphenyl)-3-(2-methoxy-methyl-4,6-dimethoxy-phenyl)-propene with AD-mix-α or AD-mix-β in the presence of methanesulfonamide, followed by acid catalysed cyclization, afforded the four catechin diastereomers in high enantiomeric excesses and yields.

Enantioselective synthesis of flavonoids. Part 51. Poly-oxygenated β-hydroxydihydrochalcones

Abstract Epoxidation of a series of poly-oxygenated chalcones with urea-hydrogen peroxide complex in THF in the presence of DBU and poly-( l )- or -( d )-leucine, followed by TBTH/AIBN catalysed ringopening, afforded β-hydroxydihydrochalcones in moderate to high enantiomeric excess and yield.

Stereoselective synthesis of flavonoids. Part 7. Poly-oxygenated β-hydroxydihydrochalcone derivatives

Abstract Epoxidation of a series of poly-oxygenated chalcones with urea-hydrogen peroxide complex in THF in the presence of DBU and poly-( l )- or -( d )-leucine, followed by TBTH/AIBN catalysed ring opening, afforded β-hydroxydihydrochalcones in moderate to high enantiomeric excess and yield. This represents the first stereoselective route towards this group of flavonoids. Epoxidation of a series of poly-oxygenated chalcones with urea-hydrogen peroxide complex in THF in the presence of DBU andpoly-(L)-or-(D)-leucine, followed by TBTH/AIBN catalysed ring opening, afforded β-hydroxydihydrochalcones in moderate to high enantiomeric excess and yield. This represents the first stereoselective access to this group of flavonoids Download : Download full-size image

Enantioselective synthesis of flavonoids. Part 3.1trans- and cis-Flavan-3-ol methyl ether acetates

Asymmetric dihydroxylation of a series of polyoxygenated 1,3-diarylpropenes with AD-mix-α or AD-mix-β in the presence of methanesulfonamide and subsequent acid-catalysed cyclization, affords for the first time synthetic access to trans- and cis-flavan-3-ol derivatives, essentially enantiopure and in good yield.

Circular Dichroic Properties of Flavan-3-ols

CD data of all four diastereoisomers of the permethylaryl ether 3-O-acetyl derivatives of a series of flavan-3-ols permit assignment of the absolute configuration at the stereocentres of the heterocyclic ring.

Dibutylboron triflate promoted conjugate addition of benzylic and allylic organocopper reagents to chiral α,β-unsaturated N-acyl imidazolidinones

Abstract The organocopper-Lewis acid system, RCu-TMEDA-Bu 2 BOTf, is useful for conjugate addition to highly constrained chiral α,β-unsaturated N-acyl imidazolidinones. In comparison with the corresponding TMSCl-activated reagents, Bu 2 BOTf exhibits a dramatic increase in reactivity during 1,4-addition of benzylic and allylic organocopper reagents, which react more readily with crotonoyl-, and especially cinnamoyl imides.

Stereoselective Synthesis of Flavonoids. Part 8. Free Phenolic Flavan-3-ol Diastereoisomers

Asymmetric dihydroxylation of a series of poly-O-methoxymethyl-1,3-diarylpropenes with AD-mix-α or AD-mix-β and subsequent acid-catalyzed cyclization of the intermediate syn-diols permits the first synthetic access to all four diastereoisomers of free phenolic flavan-3-ols in high enantiomeric excess and yield.

The first enantioselective synthesis of trans- and cis-dihydroflavonols

Epoxidation of a series of polyoxygenated chalcones with H2O2 in the presence of poly(α-amino acid) catalysts, followed by Lewis acid-catalysed phenylmethanethiol ring-opening and cyclization, afforded trans- and cis-dihydroflavonols in moderate to high enantiomeric excess and yield.

Improved synthesis for the rodenticides, diphenacoum and brodifacoum

An improved synthesis of the 3-[3-(p-substituted phenyl)-1,2,3,4-tetrahydro-1-napththyl]-4-hydroxycoumarins, diphenacoum and brodifacoum, is described. The process is primarily based on the formation of one of the crucial bonds in the carbon backbone using organocopper methodology, and on the coupling of the 4-hydroxycoumarin moiety to the 3-biphenyl tetralin unit under strongly acidic conditions.

Oligomeric isoflavonoids. Part 4.† Synthesis of the daljanelin class of isoflavonoid–neoflavonoid dimers

A protocol of introducing an electrophilic C1 fragment to a pterocarpan nucleus, followed by anionic coupling of a C6–C2 benzofuranoid precursor and late introduction of the final C6 fragment, permitted the syntheses of daljanelins B 3 and D 5. The feasibility of introducing the same electrophilic C1 fragment to C-2 of the pterocarpan moiety to obtain a precursor to daljanelin A 2 was also demonstrated.