Improved procedure for the bimolecular oxidative amidation of phenols

Silver-Catalyzed para-Selective Amination and Aminative Dearomatization of Phenols with Azodicarboxylates in Water

An efficient silver-catalyzed para-selective amination and aminative dearomatization of phenols with azodicarboxylates was developed. It afforded the para-aminophenols or amino cyclohexadieneones from free phenols depending on whether it has a para-substituent. The reaction proceeded smoothly in water under simple and mild conditions, giving the highly selective products in good yields within a short reaction time. It also showed broad substrate scope and good functional group compatibility.

Synthetic studies on heterocyclic natural products

This paper highlights ongoing efforts toward Erythrina alkaloids, himandrine, tetrodotoxin, and thiopeptide antibiotics such as nosiheptide and describes representative spinoffs in biomedicine that emanated from the author’s research in synthetic organic chemistry.

Indium(III)-catalyzed reductive bromination and iodination of carboxylic acids to alkyl bromides and iodides: scope, mechanism, and one-pot transformation to alkyl halides and amine derivatives

Highly effective indium(III)-catalyzed reductive bromination or iodination of a variety of carboxylic acids with 1,1,3,3-tetramethyldisiloxane (TMDS) and a source of bromine or iodine is described. This functional group interconversion has high tolerance for several functional groups, such as halogens, a hydroxy group, a nitro group, an olefin part, and a sulfide moiety. This indium catalytic system is also applicable to the reductive iodination of aldehyded, acyl chlorides, and esters. Furthermore, this reducing system can be applied to the one-pot synthesis of alkyl halides and amine derivatives via the addition of nucleophiles. Insight into the reaction mechanism was gained via the time course of (1)H and (13)C NMR monitoring experiments and the corresponding stepwise reactions.

Further studies toward himandrine via sequential oxidative amidation – intramolecular Diels–Alder reactions

Exploratory work toward the alkaloid himandrine evaluated the directing ability of a pyrrolidine C-3 substituent in a diastereotopic group elective intramolecular Diels–Alder reaction of a spirodienone obtained by the oxidative amidation of a phenol. The study also defined a technique for the construction of ring D of the alkaloid.

The chemical synthesis of tetrodoxin: an ongoing quest

This contribution reviews all the synthetic work on tetrodotoxin that has appeared in the literature through June 2011.

A strategy for the late-stage divergent syntheses of scyphostatin analogues

This account details the synthesis of two scyphostatin analogues exhibiting a reactive polar epoxycyclohexenone core and various amide side chains outfitted for late-stage chemical derivatization into the desirable lipophilic tails. Our efforts highlight a key ipso-dearomatization process and provide new insights regarding the incompatibility and orthogonal reactivity of scyphostatin's functional groups. We further showcase the utility of resorcinol derived 2,5-cyclohexadienones as synthetic platforms capable of participating in selective chemical reactivity, and we further demonstrate their potential for rapid elaboration into complex structural motifs.

Oxidative spirocyclization of phenolic sulfonamides: scope and applications

A full account of the oxidative dearomatization of para- and ortho-phenolic sulfonamides is provided together with an overview of the chemistry of the products and their elaboration to building blocks for spirocyclic alkaloids. A concise total synthesis of putative lepadiformine complements the discussion.

Forming spirocyclohexadienone-oxocarbenium cation species in the biomimetic synthesis of amomols

The oxidation of appropriate 2-(4-hydroxyphenyl)ethyl ketones gives direct access to amomols by means of the formation of a transient spirocyclohexadienone-oxocarbenium ion that is intermolecularly intercepted by an alcohol. Furthermore, homochiral amomols and other new analogues were synthesized for the first time and were biologically evaluated on Plasmodium falciparum.

Oxidation of α-oxo-oximes to nitrile oxides with hypervalent iodine reagents

Upon reaction with PhI(OAc)(2), α-oxo-aldoximes are oxidized to α-oxo-nitrile oxides, while α-oxo-ketoximes are converted into nitrile oxides via the oxidative cleavage of the carbonyl-imino σ bond. The nitrile oxides thus formed were trapped with norbornene or styrene in good yield. α,α'-Dioxo-ketoximes react less efficiently.

Tandem phenolic oxidative amidation-intramolecular Diels-Alder reaction: an approach to the himandrine core

An oxidative cyclization of dienic sulfonamides mediated by iodobenzene diacetate in TFA, followed by a tandem intramolecular Diels-Alder reaction, achieves desymmetrization of a "locally symmetrical" dienone with good levels of diastereoselectivity and leads to valuable synthetic intermediates for the himandrine alkaloids.

Approach to tetrodotoxin via the oxidative amidation of a phenol

An approach to tetrodotoxin that relies on the oxidative amidation of methyl 4-hydroxyphenylacetate as a key step is described. The stereoselective introduction of a beta-hydroxynitrile functionality on one of the double bonds of the emerging dienone is achieved through an intramolecular nitrile oxide cycloaddition-fragmentation sequence.

Oxidation of oximes to nitrile oxides with hypervalent iodine reagents

Iodobenzene diacetate in MeOH containing a catalytic amount of TFA efficiently oxidizes aldoximes to nitrile oxides. The latter may be trapped in situ with olefins in a bimolecular or an intramolecular mode. The new method enables the execution of tandem oxidative dearomatization of phenols/intramolecular nitrile oxide cycloaddition sequences leading to useful synthetic intermediates.

Expeditious total syntheses of natural allenic products via aromatic ring umpolung

Concise diastereoselective syntheses of the marine (+/-)-panacene and terrestrial (+/-)-desbromopanacene have been achieved in a few steps based on a concept of "aromatic ring umpolung". The synthetic avenue to the (+/-)-panacene involved a novel oxymercuration strategy to produce the correct configuration of the bromoallene moiety.