A Catalytic Method for Converting Vinylic Furanoses into Cyclopentenones

Asymmetric total synthesis of prostaglandin C2 TBS ether

We disclose an asymmetric total synthesis of prostaglandin C₂ TBS ether, a derivative of an extremely sensitive natural prostaglandin C₂. The key to the synthesis is a SmI₂-mediated ketyl-enoate reaction that leads to the formation of the functionalized cyclopentane ring with high-level stereochemical control. Access to the crucial alkene system is realized late in the synthesis by the implementation of a Grignard addition/dehydration/metathesis sequence.

Study of the β-oxygen effect in the Barton–McCombie reaction for the total synthesis of (4R,5R)-4-hydroxy-γ-decalactone (Japanese orange fly lactone): a carbohydrate based approach

Efficient and facile synthesis of Japanese orange fly lactone (1) was achieved from a commercially available d-glucose by investigating the Barton–McCombie reaction with furanose anomeric isomers (12α, β) with an overall yield of 12.6%. During the course of this synthesis, the β-oxygen effect was discovered in the deoxygenation step at the C-3 position using the Barton–McCombie reaction, where the substrate allows the effect to operate in one of the isomers but not in the other. Under the same reaction conditions, xanthate derived from the β-furanose isomer affords a high yield of deoxygenated product, whereas the α-isomer produces a very low yield. The key transformations used were Wittig olefination, TEMPO mediated oxidation, and Barton–McCombie deoxygenation, resulting in a concise total synthesis of Japanese orange fly lactone (1). Our success will allow for further biological studies of this natural product, as well as opportunities for developing new potentially promising pheromones.

The Japanese orange fly lactone was synthesised with a chiral pool approach using commercially available, starting material d-glucose. This synthesis encountered a dominant structurally functioning impact in the Barton–McCombie reaction known as the β-oxygen effect.

Serendipitous One-Step Synthesis of Cyclopentene Derivatives from 5'-Deoxy-5'-heteroarylsulfonylnucleosides as Nucleoside-Derived Julia-Kocienski Reagents

A serendipitous one-step transformation of 5'-deoxy-5'-heteroarylsulfonylnucleosides into cyclopentene derivatives is reported. This unique transformation likely proceeds via a domino reaction initiated by α-deprotonation of the heteroaryl sulfone and subsequent elimination reaction to generate a nucleobase and an α,β-unsaturated sulfone that contains a formyl group. The Michael addition of the nucleobase to the α,β-unsaturated sulfone and the subsequent intramolecular Julia-Kocienski reaction eventually generate the cyclopentene ring. Heteroarylthio and acylthio groups can be incorporated into the cyclopentene core in place of the nucleobase by conducting this reaction in the presence of a heteroarylthiol and a thiocarboxylic acid, respectively. cis,cis-Trisubstituted cyclopentene derivatives are obtained as a single stereoisomer from ribonucleoside-derived Julia-Kocienski sulfones.

Silylated Sugars – Synthesis and Properties

Silicon has been used in carbohydrate chemistry for half a century, but mostly as a protective group for sugar alcohols. Recently, the use of silicon has expanded to functionalization via C–H activation, conformational arming of glycosyl donors, and conformational alteration of carbohydrates. Silicon has proven useful as more than a protective group and during the last one and a half decades we have demonstrated how it influences both the reactivity of glycosyl donors and stereochemical outcome of glycosylations. Silicon can also be attached directly to the sugar C-backbone, which has even more pronounced effects on the chemistry and properties of the molecules. In this Account, we will give a tour through our work involving silicon and carbohydrates.

1 Introduction

2 Conformational Arming of Glycosyl Donors with Silyl Groups

3 Silyl Protective Groups for Tethering Glycosyl Donors

4. Si–C Glycosides via C–H Activation

4.1 C–H Activation and Oxidation of Methyl 6-Deoxy-l-glycosides

4.2 Synthesis of All Eight 6-Deoxy-l-sugars

4.3 Synthesis of All Eight l-Sugars by C–H Activation

4.4 Modification of the Oxasilolane Ring

5 C–Si in Glycosyl Donors – Activating or Not?

6 Si–C-Substituted Pyranosides

7 Perspective

Mechanochemical Gold(III)-Carbon Bond Formation

Starting from a [(MeO C^N^C)AuCl] complex as precursor, a direct substitution by C,H-activation from sp-, sp2 - or sp3 -C,H-bonds under basic conditions in a planetary ball mill was achieved. Because of the extraordinary photophysical properties of the target compounds, this protocol provides an easy access to a highly valued complex class. In contrast to existing protocols, no pre-functionalization of the starting materials is necessary and the use of expensive transition metal catalysts can be avoided, which makes this application appealing also for industrial purposes. In addition the methodology was not restricted to pincer complexes, which was demonstrated by the substitution of chelate type [(tpy)AuCl2 ] complexes.

Reactivity, Selectivity, and Synthesis of 4-C-Silylated Glycosyl Donors and 4-Deoxy Analogues

A method for introducing dimethylphenylsilyl at the 4-position in carbohydrates has been developed. Two C-silylated glycosyl donors were prepared via levoglucosenone, starting from cellulose. The glycosylation properties were studied using three glucoside acceptors, a 3-OH, 4-OH, and 6-OH. Compared with the 4-deoxy variant, it was found that the anomeric selectivity was influenced more by the C-2 substituents orientation than the silyl in the 4-position. In general, the reactivity of these donors was higher than the corresponding 4-deoxy-analogue, albeit a competition experiment showed that the introduction of a C-Si increases the relative reactivity by a modest factor of around two.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Mg(OMe)2 promoted allylic isomerization of γ-hydroxy-α,β-alkenoic esters to synthesize γ-ketone esters

This work concerns the Mg(OMe)₂ promoted allylic isomerization of γ-hydroxy-α,β-alkenoic esters with TMEDA as an additive. The isomerization proceeded under mild conditions and afforded γ-keto esters in high yield (up to 96%) within 2 h. Both (Z)- and (E)-γ-hydroxy-α,β-alkenoic esters were tolerated under the reaction conditions. This transformation involves the in situ formation of a dienolate intermediate from the easily accessible γ-hydroxy-α,β-alkenoic ester. The in situ generated dienolate can react with benzaldehyde and undergo a practical, useful tandem allylic isomerization-Aldol reaction to afford more functionalized compounds.

Essential reactive intermediates in nucleoside chemistry: cyclonucleoside cations

DFT-based modeling as well as experimental examination of model keto nucleosides have revealed that high susceptibility of these compounds to acids is due to formation of intermediate cyclonucleoside cations of low energy. Theoretically established chemical structures of these previously overlooked intermediates explain the reaction courses for a cluster of nucleoside reactions.

Homogeneous photocatalytic reactions with organometallic and coordination compounds--perspectives for sustainable chemistry

Since the time of Giacomo Ciamician at the beginning of the 20th century, photochemical transformations have been recognized as contributing to sustainable chemistry. Electronic excitation significantly changes the reactivity of chemical compounds. Thus, the application of activation reagents is frequently avoided and transformations can be performed under mild conditions. Catalysis plays a central role in sustainable chemistry. Stoichiometric amounts of activation reagents are often avoided. This fact and the milder catalytic reaction conditions diminish the formation of byproducts. In the case of homogeneous catalysis, organometallic compounds are often applied. The combination of both techniques develops synergistic effects in the sense of "Green Chemistry". Herein, metal carbonyl-mediated reactions are reported. These transformations are of considerable interest for the synthesis of complex polyfunctionalized compounds. Copper(I)-catalyzed [2+2] photocycloaddition gives access to a large variety of cyclobutane derivatives. Currently, a large number of publications deal with photochemical electron-transfer-induced reactions with organometallic and coordination compounds, particularly with ruthenium complexes. Several photochemically induced oxidations can easily be performed with air or molecular oxygen when they are catalyzed with organometallic complexes. Photochemical reaction conditions also play a certain role in C-H activation with organometallic catalysts, for instance, with alkanes, although such transformations are conveniently performed with a variety of other photochemical reactions.

Toward palau'amine: Hg(OTf)2-catalyzed synthesis of the cyclopentane core

Catalytic cyclization: The Hg(OTf)2‐catalyzed N‐selective cyclization of amide carbonyl moieties for the construction of a quaternary carbon center was developed. The Hg(OTf)2‐catalyzed cyclization of cyclopentylidene alcohol with acylhydrazide afforded the desired cyclopenta[c]pyridazinone in good yield. The subsequent eight steps gave the functionalized cyclopentane with the correct stereochemistry that corresponds to the E ring of palau′amine (see scheme).magnified image

Natural compounds: leads or ideas? Bioinspired molecules for drug discovery

In this article, we compare drugs of natural origin to synthetic compounds and analyze the reasons why natural compounds occupy a place of choice in the current pharmacopoeia. The observations reported here support the design of synthetic compounds inspired from plant alkaloids and their biosynthetic pathway. Our reasoning leads to very efficient syntheses of compounds which complexity matches that of indolomonoterpenic alkaloids.