A benzannulation sequence featuring [6π + 4π] cycloaddition of (η6-thiepin 1,1-dioxide)tricarbonylchromium(0) complexes with highly substituted dienes followed by Ramberg−Backlund rearrangement has...

Studies on chromium(0)-promoted higher-order cycloaddition-based benzannulation. total synthesis of (+)-estradiol

3-Acylindolizines (5a–5f) and their benzo- analogues 1-acylpyrrolo[1,2-a]quinolines (6a–6f) and 1-acylpyrrolo[2,1-a]isoquinolines (7a–7i) are regioselectively synthesized by a convenient one pot reaction of the corresponding pyridinium (quinolinium, isoquinolinium) ylide with maleic anhydride (MA) in the presence of the mild oxidant tetrakispyridinecobalt(II) dichromate (TPCD). These reactions proceed via a tandem reaction sequence of 1,3-dipolar cycloaddition of azomethine ylide with MA, anhydride hydrolysis and oxidative bisdecarboxylation of the primary cycloadducts followed by dehydrogenative aromatization of the dihydroindolizines. TPCD serves as both decarboxylation and dehydrogenation reagent in the reactions. These results show that TPCD is a promising new reagent for bisdecarboxylation of aliphatic carboxylates.

Regioselective synthesis of 3-acylindolizines and benzo- analogues via 1,3-dipolar cycloadditions of N-ylides with maleic anhydride

The 2,2‘-biindole core of ditryptophan cross-links is prominent in the fascaplysins and the indolocarbazole glycoside natural products. N-Acyliminium ions derived from the C-terminus of ditryptophan peptides cyclize in one of two modes:  N-alkylation or C-alkylation. The surrounding peptide offers some control over the course of the cyclization and allows the preparation of homofascaplysin C or indolo[2,3-a]carbazole. These targets are modest, but they are generated through carbocyclic intermediates rich in stereochemistry, and decidedly non-peptide in character.

Synthesis of Homofascaplysin C and Indolo[2,3-a]carbazole from Ditryptophans

An enantioselective synthesis of 12-epi-PGF2α (3) and 12,15-diepi-PGF2α (4), PG-like compounds that are probably generated in vivo by nonenzymatic, free-radical-induced peroxidation of arachidonic acid, has been achieved starting from the commercially available Corey lactone (9). The key strategy involves SmI2 reduction of the γ,δ-epoxy-α,β-unsaturated ester 7, followed by in situ trapping with hexanal; subsequent hydrogenation and decarboxylation affords the stereoselective construction of the lower side chain. This new method is expected to provide a convenient access to various PG-like isoprostanes derived from oxidation of arachidonic acid and cis-4,7,10,13,16,19-docosahexaenoic acid.

Enantioselective Synthesis of 12-epi-PGF2α and 12,15-diepi-PGF2α

Novel 5-X-substituted-2-azabicyclo[2.1.1]hexanes (X = 5-syn-Cl, -Br, -I, -Ph, -NHCOOR (R = Me, Bn, t-Bu), -CH2CH2COOMe and X = 5-anti-Br, -I, -Ph) were synthesized from the X = 5-syn-carboxy derivative. New 5-anti-X-2-azabicyclo[2.1.1]hexanes, X = NHCOOR (R = Me, Bn), were prepared stereoselectively from the X = 5-anti-carboxy substrate.

M. I. Katzin

Papers

An Improved Preparation of Alkyl ω-Alkenoates by Oxidative Decarboxylation of ω-Alkoxycarbonylalkanoic Acids