Efficient syntheses of rugulosin analogues

Oxidation of 3b or 14c,d with Pb(OAc)4 in AcOH for 20 min at 25 degrees C and 1 h at 75 degrees C gave flavoskyrin-type dimers 6b and 15c,d in 53-86% yield. Heating a solution of 6b or 15c,d in pyridine under air for 1 h at 75-80 degrees C and then for 1-2 h at 110 degrees C afforded rugulosin-type dimers 10b and 17c,d in 61-88% yield. This two-step sequence provides a practical route to this unusual natural product skeleton.     

Total syntheses of amythiamicins A, B and C

Total syntheses of the thiopeptide antibiotics amythiamicins A, B and C are reported.     

Total syntheses of furaquinocin A, B, and E

A modular approach to the total synthesis of furaquinocins culminated in the total syntheses of furaquinocin A, B, and E. A Pd-catalyzed dynamic kinetic asymmetric transformation (DYKAT) on carbonates derived from Baylis-Hillman adducts, followed by a reductive Heck cyclization allows the enantio- and diastereoselective construction of dihydrobenzofuran 32. Introduction of a double unsatured side chain via Horner-Wadsworth-Emmons reaction and assembly of the naphthoquinone with squaric acid based methodology leads to furaquinocin E. The use of differentially substituted squaric acid derivatives allows the synthesis of three analogues of furaquinocin E. The additional stereocenters in furaquinocin A and B can be introduced with a diastereoselective Sakurai allylation. The stereoselective elongation of the side chain is possible using cross metathesis or ring closing metathesis. The obtained late-stage intermediates were successfully transformed to furaquinocin A and B.     

Total syntheses of arenamides A,B and C

Total syntheses of the three arenamides A–C, NFκB inhibitors, are described for the first time. The key steps involved in the synthesis are a Crimmin’s aldol, Wittig olefination and a macrolactamization reaction.     

Total syntheses of Tardioxopiperazine A, Isoechinulin A, and Variecolorin C

First total syntheses of the isoechinulin-type alkaloids: Tardioxopiperazine A, Isoechinulin A, and Variecolorin C have been achieved from a common key intermediate 5, which was derived from a regiocontrolled Stille cross-coupling reaction of an allylindium reagent.     

Total syntheses of subereamollines A and B

The first total syntheses of (+)- and (-)-subereamollines A and B are reported. The enantiomeric forms of the natural products were obtained by preparative chiral HPLC separation of the corresponding racemates.     

Total syntheses of anominine and tubingensin A

A divergent strategy for the total syntheses of the indole terpenoid anominine (1) and its natural congener tubingensin A (2) has been developed. The common intermediate 11 bearing all of the required stereogenic centers for both natural products was first assembled by employing a Ueno-Stork radical cyclization and a Sc(OTf)(3)-mediated Mukaiyama aldol reaction to form the key C-C bonds in a stereocontrolled manner. The route to anominine features a radical deoxygenation followed by an efficient side-chain installation, while the path to tubingensin A exploits a CuOTf-promoted 6π-electrocyclization/aromatization sequence to forge the central region of the pentacyclic scaffold.     

Total syntheses of ent-heliespirones A and C

Stereodivergent total syntheses of ent-heliespirone A and C were both completed in 11 vessels and ～24% combined overall yield (A + C). These syntheses employed an identical inverse demand Diels-Alder reaction between a surrogate for an extendedly conjugated γ-δ unsaturated ortho-quinone methide and L-lactic-acid-derived exocyclic enol ether. Novel reactions of special note include a diastereoselective reduction of a chroman spiroketal by combination of borontrifluoride etherate and triethyl silane, along with oxidative rupture of a chroman etherial ring into the corresponding p-quinone by argentic oxide (AgO). In addition, an unusual intramolecular etherification of a 3° alcohol caused by cerium ammonium nitrate was observed.     

Total syntheses of graphisin A and sydowinin B

Efficient syntheses of the highly substituted benzophenone graphisin A and the xanthone sydowinin B are described. Key steps involve aryl anion addition to substituted benzaldehyde derivatives, subsequent methyl ester installation, and dehydrative cyclization. Oxidation of graphisin A led to a spirodienone derived from a highly substituted benzoquinone intermediate.     

Total syntheses of the strobilurins G, M, and N

The key reactions in the general synthesis of strobilurins are the highly (Z)-selective Wittig reaction of an (E)-cinnamaldehyde with the phosphorus ylide 8 derived from (1,1-dibromoethyl)triphenylphosphonium bromide, followed by bromine-iodine exchange and Pd-Cu co-catalyzed Stille cross-coupling of the resulting alkenyl iodide with methyl (Z)-2-tributylstannyl-3-methoxyacrylate (7). The synthetic strobilurins G, M, and N were identical with the corresponding natural compounds. In addition, the (2′ S)-configuration of strobilurin G (1) was unambiguously established by oxidative degradation of the synthetic intermediate (S)-9 to (R)-2,3-dihydroxyisovaleric acid.     

Total syntheses of (-)-fumiquinazolines A, B, and I

[structure] The first total syntheses of (-)-fumiquinazolines A, B, and I have been accomplished efficiently using the Pd-catalyzed cyclization of an iodoindole carbamate to construct the imidazoindolone moiety and the dehydrative cyclization of a diamide followed by rearrangement through an amidine to construct the quinazolone moiety.     

Total syntheses of the proposed structures of cuevaene A

Two proposed structures of cuevaene A were synthesized and the NMR spectra of both structures are proved to be inconsistent with those of the natural product. The structure of cuevaene A is still unclear and needs to be revised.     

Direct, regioselective synthesis of 2,2-dimethyl-2H-chromenes. Total syntheses of octandrenolone and precocenes I and II

Herein is reported an efficient method for the synthesis of 2,2-dimethyl-2H-chromenes in a single step from the corresponding phenol and 3-methyl-2-butenal via microwave irradiation in CDCl₃. This protocol features a mild reaction environment (neutral, no added catalyst) which yields regioselective formation of the chromene and displays tolerance toward acid- and base-sensitive protecting groups.     

Total syntheses of eburnamonine,quebrachamine, vincadine and epivincadine

Syntheses of the alkaloids eburnamonine and quebrachamine are presented in which the non-tryptamine portion of the skeleta is constructed by the β-oxycyclopropylcarboxylate preparation-fragmentation route. A similar reaction scheme is utilized for the synthesis of the alkaloids vincadine and epivincadine.     

Total syntheses of dehydrobotrydienal,dehydrobotrydienol and 10-oxodehydrodihydrobotrydial

Concise total syntheses of dehydrobotrydienal, dehydrobotrydienol, and 10-oxodehydrodihydrobotrydial were accomplished via tandem Pauson–Khand and 6π-electrocyclization reactions.     

Total syntheses of the marine pyrrole alkaloids polycitone A and B

Polycitone B (2) was obtained in four steps from pyrrole dicarboxylic acid 3, including Friedel-Crafts reaction of the corresponding acid chloride with anisole. The conversion of 2 into polycitone A (1) was achieved in two steps via Mitsunobu alkylation of the pyrrolic NH group. The synthesis of polycitone A proceeds in 18% overall yield and offers the possibility of varying the substituents on the pyrrole ring.