György Litkei

Absolute configuration and total synthesis of (−)-cabenegrin A-I

Abstract The total synthesis of (−)-cabenegrin A-I [(−)- 1 ] in five steps was achieved from (−)-6a R ,11a R -maackiain [(−)- 5 ], which in turn was prepared by the optical resolution of racemic (±)- 5 using S -(−)- α -methylbenzyl isocyanate as the the chiral auxiliary. The homochirality of (−)-maackiain [(−)- 5 ] and (−)-cabenegrin A-I [(−)- 1 ] was proved by CD measurements. Synthesis of (±)-maackiain [(±)- 5 ] is also presented, starting from the readily available phenol derivatives resorcinol and sesamol, which demonstrates the synthetic utility of the Heck-type oxyarylation process for obtaining pterocarpane derivatives on a multigram scale. A new ring-opening reaction of pterocarpanes (7 → 28) is described.

Reactions of 2′-NHR-Chalcone Dibromides with Ammonia

Abstract Synthesis of 2′-NHR-chalcone dibromides and their reaction with methanolic ammonia are discussed. Depending on the character of the R group, ethylenimine, -bromochalcone, 2,3-dimethoxypropan-1-one and 1,2,3,4-tetrahydro-4-quinolone derivatives were obtained.

Flavonoids, 40.+ Synthesis of 3-alkyl- and -arylthioflavanones and their transformations into sulfur-containing flavonoids

Abstract trans -3-Mesyloxyflavanones 1 were converted into cis - and trans -3-(alkylthio)- and -(phenylthio) flavanones 2 - 4 by nucleophilic substitution reaction with thiols or thiolates. Flavanones 2 - 4 were useful intermediates in the synthesis of various sulfur-containing derivatives; flavanones, flavones and dihydrochalcones possessing alkyl- or arylthio, -sulfinyl and -sulfonyl group. Oxidation of cis - and trans - isomers of 4 led to completely different products.

Flavonoids, 39. The reaction of 3-mesyloxyflavanones with O- and S-nucleophiles, synthesis of 3-thiocyanato- and 3-acetylthio-flavanones

Abstract The action of either cyanate or acetate ions on trans -3-mesyloxyflavanones 1 led to the formation of flavones 2 and aurones while the reaction with the respective S-nucleophiles (thiocyanate and thioacetate ions) resulted in cis -and trans -3-thiocyanato- and 3-acetylthioflavanones ( 6 and 11 ). The participation of the concurrent nucleophilic substitution, β-elimination and elimination with ring-contraction is dependent on the “hard-soft” character of the nucleophile and the increase of the “soft” character favours the displacement.

Oxidation of the 2′-NHR Analogues of 2′-OR-Chalcones; Conversion of 2′-NHR-Chalcone Epoxides

Abstract Synthesis of 2′-NHR-chalcone expoxides and their reaction with acidic reagents are discussed.

Reaction of chalcones with NBS, a simple one pot synthesis of 2-aroylbenzo[b]furanes

Abstract A simple one pot synthesis of 2-aroylbenzo[b]furanes has been achieved by bromomethoxylation with NBS and subsequent treatment of the appropriately substituted 2-hydroxychalcones with sodium hydroxide.