From p-benzoquinone to useful chiral cyclohexane building blocks

A straightforward and efficient access to 12 new cyclohexane chirons from an easily available enantiopure monoketal of p-benzoquinone is described. These chirons possess a variety of functional groups which render them useful for further synthetic elaboration.     

New oxazole-based peptidomimetics: useful building blocks for the synthesis of orthogonally protected macrocyclic scaffolds

[structure: see text] The synthesis of a new family of densely functionalized oxazole-containing amino acids is described. These building blocks were employed for preparing macrocycles containing Lys and Glu residues by a combination of solid- and solution-phase synthesis. The resulting structures are presented as orthogonally protected scaffolds for supramolecular chemistry.     

Regioselective entry to bromo-gamma-hydroxybutenolides: useful building blocks for assemblying natural product-like libraries

[reaction: see text] We report a regioselective entry to 3-bromo- and 4-bromo-5-hydroxy-5H-furan-2-ones by photooxidation of 3-bromofuran with a singlet oxygen in the presence of a suitable base. By this procedure, a variety of 3-substituted gamma-hydroxybutenolides have become for the first time easily accessible. Strategies employing these highly functionalized building blocks for the preparation of focused libraries of natural-like molecules are also discussed.     

The aza-achmatowicz rearrangement: A route to useful building blocks for N- containing structures

N-Acyl 2-furylamines were transformed into 2-alkyl-6-methoxy-hexahydropyridin-3-ones. The rearranged products are useful building blocks for the total synthesis of alkaloids and unusual aminoacids.     

Fluorination of α,α-dichlorosulfides: access to gem-difluorothioethers as useful building blocks

The synthesis of alkylsulfanyldifluoro-acetate and ketones by the Halex reaction is described. The remarkable reactivity of thiodifluoroacetate derivatives opened rapid access for the preparation of useful building blocks such as gem-difluoroketones and amides.     

Synthesis of porphyrazines bearing thioalkylthiol tethers: useful building blocks for supramolecular chemistry

A simple and substantially inexpensive method is proposed for the synthesis of a porphyrazine macrocycle symmetrically functionalized with eight bromoalkylthio pendants and its conversion in the S-acetyl protected thiol-hexylthio-substituted analog.     

Simple preparations of 4 and 5-iodinated pyrazoles as useful building blocks

The pyrazole nucleus has recently become a recurrent scaffold in the research fields of CropScience and oncology. We report here the preparation of an array of 4- and 5-iodinated pyrazole derivatives, such as 4-iodo-3-trifluoromethylpyrazole or ethyl 5-iodo-4-carboxy-3-trifluoromethylpyrazoles. This work provide access to many new pyrazole derivative, including 11 original out of 16 iodinated building blocks, thus opening accesses to new chemical entities featuring a pyrazole nucleus.     

Synthesis of useful building blocks for monofluorinated compounds derived from trifluoroethene

A synthetic approach to monofluorinated compounds starts from the Friedel-Crafts acylhalogenation of trifluoroethene to give chlorotrifluoroketones and thence trifluorovinyl ketones. These are converted to phenylthio-adducts and thence monofluorinated α, β-unsaturated phenylthioesters, which by reduction afford β-fluoroallylic alcohols.     

New chiral building blocks from tetrabromocyclopropene and furan

The cyclocondensation of tetrabromocyclopropene and furan leads directly to a halogenated oxabicyclo[3.2.1]octadiene derivative. Over the past several years, we have utilized these compounds as intermediates for natural product synthesis. Herein, we describe the preparation of nonracemic dibromoenone building blocks from the racemic cycloadduct. Conversion of the adduct to a mixture of tartrate-derived ketals followed by separation of the diastereomers and hydrolysis allows for the formation of novel chiral synthons with either absolute configuration.     

New isocysteine building blocks and chemoselective peptide ligation

Boc-, Fmoc- and Cbz-protected isocysteine building blocks were prepared by a concise three-step procedure starting from thiomalic acid. The use of Boc/Trt-protected isocysteine provided convenient access to isocysteinyl peptides that allow the chemoselective ligation of unprotected peptide fragments in water. The pH-dependency of the isocysteine-mediated ligation was compared with that of cysteine-mediated native chemical ligation.     

Trihaloacetaldehyde N,O-acetals: useful building blocks for dihalomethylene compounds

The reaction of trifluoroacetaldehyde N,O-acetals with more than 2 equiv of alkyllithiums at −78 °C resulted in regiospecific defluorinative alkylation with unusual regioselectivity to give α,α-difluoroketone N,O-acetals in excellent yield. In contrast, under similar conditions, trichloroacetaldehyde N,O-acetals gave simple mono-dechlorinated product without the alkyl transfer reaction from alkyllithiums to the generated intermediates.     

LIC-KOR promoted formation of conjugated dienes as useful building blocks for palladium-catalyzed syntheses

It is demonstrated that α,β-unsaturated acetals can be considered a synthetic tool for transforming carbonyl derivatives into cheap and easily accessible starting materials for the construction of various and more complex structures. The lithium-potassium mixed superbase LIC-KOR induces a conjugate elimination reaction that converts α,β-unsaturated acetals into 1E-1-alkoxybuta-1,3-dienes. These derivatives can be readily metalated in situ and functionalized by reaction with electrophiles. The results can be grouped in two sections: (1) the palladium-catalyzed cross-coupling reaction between alkoxydienylboronates and tetralone- or isochromanone-derived vinyl triflates; (2) the regio- and stereoselective cross coupling reaction with aryl derivatives in the presence of a palladium catalyst (Heck conditions).     

Naphthalene-1,8-diyl bis(halogenophosphanes): novel syntheses and structures of useful synthetic building blocks

A series of new bay region disphospha-functionalised naphthalenes is reported. The reduction of ylidic phosphonium phosphoride NapP(2)Cl(6) (1) (Nap=naphthalene-1,8-diyl) with MeOPCl(2) gives the important synthon Nap(PCl(2))(2) (2) in nearly quantitative yield. Reaction of 1 with magnesium metal affords (NapP(2))(n) (3), which reacts with Br(2) and I(2), yielding Nap(PBr(2))(2) (4) and Nap(PI)(2) (5), respectively. X-ray structure determinations reveal a twisted geometry of the naphthalene ring in sterically strained 2 and 4, whilst the presence of a P-P bond in 5 results in the release of the steric strain and generation of the planar NapP(2) moiety. Although the tetrahedral P environments are severely distorted the sigma(3)P-sigma(3)P bonding in 5 represents a new type of P-P bonding environment in 1,8-diphosphanaphthalenes. Compounds 1, 4 and 5 each represent the highest coordination, achievable by direct halogenation. The new compounds 2-5 were fully characterised by NMR, IR, and Raman spectroscopy, mass spectrometry, and elemental analysis.     

New chiral building blocks of β-peptoid analogs

The synthesis of chiral functionalized β-amino esters via the hydride reductive amination of chiral allenes was explored. These compounds can be regarded as β-peptoids building blocks bearing a chiral side chain at the nitrogen and at the same time retaining the β-amino acid side chain. β-Enamino esters were obtained from the nucleophilic addition of α-amino esters (l-Ala, d-Ala, l-Phe, l-Leu, l-Trp and d-Trp methyl esters) to 2,3-allenoates bearing a chiral auxiliary, which determines the stereochemistry outcome of the subsequent reduction reaction. It was also demonstrated that in the reduction of β-enamino esters derived from l-Pro and d-Pro methyl esters the chirality of the new chiral center is controlled by the α-amino ester moiety.     

Synthesis of new ribosylated Asn building blocks as useful tools for glycopeptide and glycoprotein synthesis

We performed the first synthesis of new Asn derivatives bearing α- or β-ribose as pure anomers, linked by an N-glycosidic bond, on the side chain of the Asn residue orthogonally protected for Fmoc/^tBu SPPS, by an efficient five-step strategy with a global yield of 73% starting from d-ribose. These building blocks are obtained in a large scale and can be useful tools for glycopeptide and glycoproteins synthesis.     

Diastereoselective synthesis of useful building blocks by crotylation of beta-branched alpha-methylaldehydes with potassium crotyltrifluoroborates

The diastereoselective construction of stereotriads having consecutive methyl, hydroxy, and methyl substituents was realized by the substrate-controlled crotylation of beta-branched alpha-methylaldehydes with potassium crotyltrifluoroborates. Especially, crotylation of 2-(1,3-dithian-2-yl)propanal with potassium ( E)-crotyltrifluoroborate afforded, in good yield and with excellent diastereoselectivity, a useful building block that has different and potential functional groups on both ends.     

A renaissance of color: New structures and building blocks for organic electronics

Natural dyes and pigments like indigo and its derivatives valued for their bright colors and photochemical stability has been used since antiquity. Recently, the need for better performing materials in the organic electronics field has inspired a resurgence of these historical molecules and their subsequent transformation into new families of π‐conjugated building blocks used to construct new (macro)molecular semiconductors. This Highlight will explore the renaissance of notable building blocks including diketopyrrolopyrrole, (iso)indigo, benzodipyrrolidone, and benzodifuranone, as well as nonfullerene acceptor structures 9,9′‐bifluorenylidene and quinacridone. In addition, as the organic electronics field continues to evolve, the design of molecules with precise structure and function embodies a new paradigm for the next generation of materials. Representative examples will be described that embrace this new model and point the direction for advanced technologies. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Photoreaction of thioxanthone with indolic and phenolic derivatives of biological relevance: magnetic field effect study

The photoinduced reaction of thioxanthone (TX) with various indolic and phenolic derivatives and amino acids like tryptophan and tyrosine has been monitored in sodium dodecyl sulfate micellar medium. Laser flash photolysis and magnetic field effect (MFE) experiments have been used to study the dynamics of the radical pairs. The quenching rate constant with different quenchers in SDS micellar solution has been measured. For indoles the electron-transfer reaction has been found to be followed by proton transfer from the donor molecule, which gives rise to the TX ketyl radical. On the other hand, the electron-transfer reaction in the case of phenols is preceded with formation of a hydrogen-bonded exciplex. The extent of the MFE and magnitude of the magnetic field corresponding to one-half of the saturation value of MFE ( B 1/2) support the fact that hyperfine mechanism plays the primary role. Quenching of MFE in the presence of gadolinium ions confirms that the radical pair is located near the micellar interface. MFE study has been further extended to protein-like bovine serum albumin in micellar solution. The results indicate loss in mobililty of radical pairs in the protein surfactant complex.